Transcriber’s Notes
Obvious typographical errors have been silently corrected. Variations
in hyphenation have been standardised but all other spelling and
punctuation remains unchanged.
Italics are represented thus _italic_.
MORE MINOR HORRORS
[Illustration: Mosquitos in the Colvith River delta, Arctic Alaska,
about 71° lat., July 1909. The Eskimo, Natkusiak, had stood still for
a minute or two, and refrained from brushing them off, while loading a
uomiak. (From the _American Museum Journal_.)
[_Frontispiece_]]
MORE
MINOR HORRORS
BY
A. E. SHIPLEY, Sc.D.
HON. Sc.D. PRINCETON, F.R.S.
MASTER OF CHRIST’S COLLEGE, CAMBRIDGE, AND READER IN ZOOLOGY
IN THE UNIVERSITY
ILLUSTRATED
LONDON
SMITH, ELDER & CO., 15 WATERLOO PLACE
1916
[All rights reserved]
EDMUNDO ALFREDO CARRINGTON
ET
JOHANNI TRISTRAM YARDE
COLLEGII CHRISTI DILECTISSIMIS ALUMNIS
HUIC AB ORIENTI ILLI AB OCCIDENTI PARTE
PRO PATRIA PUGNANTIBUS
PREFACE
My publisher tells me that this volume will be regarded as a sequel
to ‘The Minor Horrors of War,’ and he assures me that sequels are
not a success. I have no doubt my publisher is right, because if
publishers were not invariably right, and authors invariably wrong, how
can one explain the fact that publishers are proverbially prosperous
and prominent people, whereas authors are notoriously penniless and
obscure? In spite of his warning, however, I propose to publish this
little volume, for there still ‘air some catawampous chawers in the
small way, too, as graze upon a human pretty strong’—as ‘one of them
inwading conquerors at Pawkins’s’ called them—that were unmentioned in
my earlier book.
I am indebted to the kindness of the Editor and Proprietors of the
_British Medical Journal_ for permission to reprint Chapters I to IX
and Chapter XI, and to the Editor of _The Journal of Economic Biology_
for permission to reprint the twelfth chapter, of this book, and I
offer them my thanks. I also thank Mr. Hugh Scott (the University
Curator in Entomology), and Professor G. H. Carpenter of the Royal
College of Science, Dublin, for much kindly help.
A. E. SHIPLEY.
CHRIST’S COLLEGE LODGE, CAMBRIDGE,
_April 1916._
CONTENTS
CHAPTER PAGE
I. COCKROACHES (_Periplaneta_) 1
II. COCKROACHES (_continued_) 16
III. THE BOT- OR WARBLE-FLY (_Hypoderma_) 25
IV. THE MOSQUITO (_Anopheles maculipennis_) 42
V. THE MOSQUITO (_continued_) 53
VI. THE MOSQUITO (_continued_) 65
VII. THE MOSQUITO (_continued_) 76
VIII. THE MOSQUITO (_continued_) 86
IX. THE YELLOW-FEVER MOSQUITO (_Stegomyia
calopus_) 101
X. THE BISCUIT-‘WEEVIL’ (_Anobium paniceum_) 111
XI. THE FIG-MOTH (_Ephestia cautella_) 114
XII. THE STABLE-FLY (_Stomoxys_) 124
XIII. RATS (_Mus_ or _Epimys_) 135
XIV. THE FIELD-MOUSE (_Apodemus sylvaticus_) 153
INDEX 161
ILLUSTRATIONS
FIG. PAGE
A portrait of the head of an Eskimo attacked by
mosquitos _Frontispiece_
1. _Periplaneta orientalis_, male, dorsal view 2
2. _P. orientalis_, male, side view 6
3. Mouth parts of _P. orientalis_ 9
4. _P. orientalis_, female, dissected 10
5. Egg capsule of _P. orientalis_ 12
6. Cast skin of the nymph stage of cockroach 18
7. Nymph stage of cockroach escaping from old skin 19
8. _Hypoderma bovis_ 29
9. Eggs of _H. lineatum_ 33
10. Eggs of _H. bovis_ 35
11. Entrance hole of _H. lineatum_ 37
12. Cow being chased by warble-fly 40
13. Side-view of head of _Anopheles maculipennis_, female 44
14. Section through proboscis of _A. maculipennis_, female 45
15. Piercing-lancets of _A. maculipennis_, female 46
16. _A. maculipennis_, female, sucking blood 58
17. _A. maculipennis_, male 66
18. Stridulating organ of _A. maculipennis_ 70
19. Larva and eggs of _A. maculipennis_ 78
20. Side view of the head of larva of _A. maculipennis_ 81
21. Under surface of head of larva of _A. maculipennis_ 82
22. Diagrams of mosquitos and gnats 85
23. Side view of pupa of _A. maculipennis_ 91
24. Tail of pupa of _A. maculipennis_ 93
25. Imago mosquito issuing from pupa-case 95
26. _Stegomyia fasciata_, female 104
27. Larva and eggs of _S. fasciata_ 106
28. Larva of _S. fasciata_ 107
29. Egg of _S. fasciata_ 108
30. The biscuit-‘weevil’ (_Anobium paniceum_) 112
31. The larval and pupal stages of _A. paniceum_ 113
32. Orchard of fig-trees 115
33. The fig-moth (_Ephestia cautella_) 116
34. Figs drying on reeds 119
35. Figs packed on strings 120
36. Pile of refuse-figs 122
37. The stable-fly (_Stomoxys calcitrans_) 125
38. _Stomoxys calcitrans_ 126
39. Wings of _Musca domestica_ and of _Stomoxys calcitrans_ 127
40. Side view of head of _Stomoxys calcitrans_ 128
41. _Stomoxys calcitrans_. Eggs 129
42. Acephalous larva of _Stomoxys calcitrans_ 130
43. Coarctate pupa of _Stomoxys calcitrans_ 131
44. The rat (_Mus rattus_) 136
45. Head of _Mus rattus_ 138
46. _Mus decumanus_ 143
47. Head of _Mus decumanus_ 145
48. The field-mouse (_Apodemus sylvaticus_) 156
49. Diagram of burrow of field-mouse 159
MORE MINOR HORRORS
CHAPTER I
COCKROACHES (_Periplaneta_)
PART I
_The Governess:_ And, perhaps, Mabel, as they are not black
and as they are not beetles, you will in future call them cockroaches.
_Mabel:_ Certainly, Miss Smith, although they are not cocks
and they are not roaches. (_Punch._)
In ‘The Minor Horrors of War,’ we rather neglected the Navy—the
senior Service, and till now the more dominant of our two magnificent
forces—partly because it is less interfered with by insect pests than
is the sister Service, though the common pests of our poor humanity—the
flea, the louse, the bug—are, like the poor, ‘always with us.’ Like
aeroplanes, insects have captured the air; like motors, they have made
a respectable show on land; but they have signally failed at sea. They
have nothing corresponding to battleships or submarines; and a certain
bug, called _Halobates_, alone hoists the insect flag on the ocean, and
that only in the warmer waters.
[Illustration: FIG. 1.—_Periplaneta orientalis_, male. × 2. Dorsal
view. 1, Antenna; 2, palp of first maxilla; 3, prothorax; 4, anterior
wings; 5, femur of second leg; 6, tibia; 7, tarsus; 8, cerci anales;
9, styles. (From Kükenthal.)]
Insects are not only highly intelligent animals, but are by far the
most numerous and dominant class of the Animal Kingdom; and they have
probably come to conclusions about themselves and the sea, comparable
to those expressed by Dr. Johnson about man and the ocean: ‘To all the
inland inhabitants of every region the sea is only known as an immense
diffusion of waters, over which men pass from one country to another,
and in which life is frequently lost.’
But one insect at least causes more trouble to sailors than to
soldiers—and that is the cockroach. Like the bed-bug, the cockroach
came into England at the end of the sixteenth century, and, like the
bed-bug, it came from the East. It seems to have been first introduced
into England and Holland in the spacious times of Henry VIII by the
cross-sea traffic, and from about the end of the sixteenth century the
cockroach began gradually to spread throughout the Western world. Like
the rat, the bed-bug, and the domestic fly, it has become thoroughly
acclimatised to human habitations, and is indeed an associate of man.
It is very rarely found living apart from some form or other of human
activity.
This insect seems to have been first described in England in
Moufet’s ‘Insectorum Theatrum,’ 1634, and he speaks of it as living
in flour-mills, wine-cellars, &c., in England, and he tells us how
Sir Francis Drake took, in 1584, the _San Felipe_, a Spanish East
Indiaman, laden with spices and burdened with a great multitude of
flying cockroaches on board.
This species was _Periplaneta orientalis_; but there is another and a
larger species, which presumably came into England from the West later
than its Eastern cousin _P. americana_—which can frequently be seen in
England running about in the cages in our zoological gardens—but it is
not on exhibition, it is a by-product, and is not counted in the fee
for admission to the gardens.
Latter tells us there are ten species of BLATTODEA which occur in
Britain; but only three of these are indigenous, and these three all
belong to the genus _Ectobia_. _Ectobias_ are smaller than cockroaches,
and do not frequent human habitations, but live in shrubs, under
rubbish heaps, &c. Some species of _Ectobia_ are, however, very
destructive and have been known to destroy in one day the whole
accumulation of dried but not properly salted fish in a Lapland
village. Of the remaining species of cockroach most are local, and
occur sporadically in particular factories, or places where food is
stored but they are not very widely spread.
As we have said above, _P. orientalis_ is the common English cockroach,
_P. americana_ occurs especially in zoological gardens and menageries;
but a third species, _P. germanica_, sometimes gets established.
Mercifully, _P. germanica_ does not seem to spread. Neither _P.
germanica_ nor _P. americana_ seem to make much headway against _P.
orientalis_, which appears to be predominant over both these other
species.
_P. germanica_ is probably most methodical, very thorough, very
brave, very faithful—but rather lacking in the power of understanding
the point of view of others. If it has any association with its
specific name, it illustrates the most striking example in the world’s
history of the divorce of wisdom from learning. ‘O Lord! give us
understanding,’ should be the prayer of _P. germanica_.
Miall and Denny tell us that from the first introduction of _P.
orientalis_ into England it took two centuries before it spread far
beyond London. In 1790 Gilbert White speaks of it as ‘an unusual
insect, which he had never observed in his house till lately,’
and, indeed, at the present moment many English villages are still
blissfully ignorant of this particular nuisance.
As Fig. 2 shows, the cockroach is a somewhat slackly put
together insect. One might almost call it rather slatternly and
loose-jointed—and the latter it certainly is. Its head moves freely on
the thorax, and the thorax on the abdomen. The successive segments
of the latter move very freely on one another. The legs are long and
mobile, and so are the antennae with which the animal is ceaselessly
testing the ground over which it flits hither and thither in its
restless activity.
[Illustration: FIG. 2.—_Periplaneta orientalis_, male. × 2. Side
view. 1, Antenna; 2, head; 3, prothorax; 4, anterior wing; 5, soft
skin between terga and sterna; 6, sixth abdominal tergum; 7, split
portion of tenth abdominal tergum; 8, cercianales; 9, styles; 10, coxa
of third leg; 11, trochanter; 12, femur; 13, tibia; 14, tarsus; 15,
claws. (From Kükenthal.)]
Cockroaches are very difficult to catch. They practically never walk,
but run with a hardly believable rapidity, darting to and fro in an
apparently erratic mode of progression. Even when caught they are
not easily retained, for they have all the slipperiness of a highly
polished billiard-ball. They have great powers of flattening their
bodies, and they slip out of one’s hand with an amazing dexterity.
Besides their slipperiness they have another weapon, and that is a
wholly unpleasant and most intolerable odour, which is due to the
secretion of a couple of glands situated on the back of the abdomen.
The glands which produce this repellent odour are sunk in the soft
membrane which unites the fifth and sixth abdominal segments, and
the moment a cockroach is attacked it exudes a sticky, glue-like
fluid, which gives out this most unendurable smell. The fluid is
extraordinarily tenacious and difficult to remove from the hand of
those who have touched the insects. No doubt the cockroach, in nature,
finds safety in this from the attacks of insectivorous animals.
Cockroaches, as has been said, very rarely walk, they nearly always
run, and they advance the first and third leg of one side at the same
time as the middle leg of the other, pulling themselves forward with
their front legs and pushing themselves forward with the hindermost.
They are thus constantly poised on a tripod. They occasionally, but not
very often, use their wings for flight. When they do so, their anterior
wings are stretched out at right angles to the body, and take no active
share in beating the air. They act in effect as monoplanes. It is the
hinder wings which really do the active flying. After a flight, the
hinder wings are shut up something in the manner of a fan.
The flattened coxae, or thighs, of the leg are adapted for shovelling
débris back from beneath the body when the insect is enlarging its
habitation. When the cockroach gets into a dusty ‘_milieu_’ the dust
is immediately removed; the hairs on the legs act as clothes-brushes
and brush every part of the body, whilst the antennae, which attract
any dust in the neighbourhood, are repeatedly drawn through the closed
mandibles and so cleaned. A cockroach is able to walk on smooth
surfaces because it possesses between the joints of the tarsus certain
soft, white patches, very velvety, and these give the creature a good
hold, and prevent slipping even on glass.
Cockroaches will eat pretty well everything. They are a great nuisance
on board ship, where they are said to gnaw the skin and nibble the
toe-nails of sailors. Hardly any animal or vegetable substance
is absent from their menu. It is said that they will even devour
bed-bugs, and that natives on the African shores, troubled by these
semi-parasites, will beg cockroaches as a favour from sailors in
passing ships.
[Illustration: FIG. 3. Mouth appendages of _Periplaneta_ (magnified).
A, Mandible. B, First maxilla: 1, cardo; 2, stipes; 3, lacinia; 4,
galea; 5, palp. C, Right and left second maxillae fused to form the
labium: 1, submentum; 2, mentum; 3, ligula, corresponding to the
lacinia; 4, paraglossa, corresponding to the galea; 5, palp. (From
Latter.)]
The mandible (Fig. 3), with its strongly toothed surface, is capable
of biting and grinding into fragments a very varied diet. The food is
moistened by the secretion of the salivary glands, which is capable of
converting starch into the more soluble sugar. The food is further
ground up by a series of hard ridges projecting into the inner face of
the gizzard (Fig. 4, 7). The secretion of the so-called hepatic caeca
is capable of emulsifying fat and rendering proteins soluble. Thus the
ordinary food substances are reduced to a condition in which they are
capable of diffusing from the lumen of the alimentary canal into the
blood which floods the body cavity.
[Illustration: FIG. 4.—A female cockroach, _Periplaneta_, with the
dorsal exoskeleton removed, dissected to show the viscera. Magnified
about 2. 1, Head; 2, labrum; 3, antenna, cut short; 4, eye; 5, crop;
6, nervous system of crop; 7, gizzard; 8, hepatic caeca; 9, mid-gut
or mesenteron; 10, Malpighian tubules; 11, colon; 12, rectum; 13,
salivary glands; 14, salivary receptacle; 15, brain; 16, ventral
nerve cord with ganglia; 17, ovary; 18, spermatheca; 19, oviduct;
20, genital pouch, in which the egg-cocoon is found; 21, colleterial
glands; 22, anal cercus. (From Latter.)]
The external movement—one might almost say ‘the panting’—which is very
obvious in the abdomen, the alternate flattening and deepening of
this part of the body, is a movement of inspiration and expiration,
the air being driven into the stigmata and so into the tracheae or
breathing-tubes. There is a considerable variation in the rate of these
pulsations, but the cockroach’s heart beats at an average rate of
seventy to eighty contractions per minute.
Although cockroaches have fairly developed eyes, they seem to trust
very largely to tactile impressions in appreciating their relations
to the surrounding world. Their antennae and the palps of their first
and second maxillae are constantly touching the surface on which they
are resting or moving, and from time to time their antennae wildly
wave in the air in a manner which suggests that they are smelling out
the external circumstances which environ them. The 39,000 sensory
‘nerve-endings’ which are found in the antennae of the male cockroach
are almost certainly olfactory in function. At the posterior end of
the body the two ‘cerci’ are also sensitive to tactile impressions, and
probably act at the hinder end of the cockroach as the antennae act at
the forward end. Cockroaches are certainly keenly sensitive to light,
and, as every one knows, they shun the light, and when detected in
daylight or candle-light they make as quickly as they can for some dark
hole or crevice in which to hide.
[Illustration: FIG. 5.—Egg capsule of _P. orientalis_ (magnified). A,
External view; B, opened; C, end view. (From Miall and Denny.)]
Cockroaches breed during the summer, and their eggs are laid in packets
of sixteen in a capsule or cocoon with rounded ends, and with an upper
corrugated edge. These cocoons are very like the little hand-bags
ladies have carried since the dressmakers denied them pockets. There
are sixteen ovarian tubes in the female, and each of these deposits
one egg in each cocoon. The ventral portion of the seventh abdominal
segment in the female is shaped like the prow of a boat, and it is in
this structure that the cocoon, or egg-case, is built up. Each egg is
fertilised by a spermatozoon which has been deposited by the male in
the spermatheca of the female. The eggs are placed in a double row,
eight in each row, facing each other, and, as they gradually develop,
it becomes apparent that the ventral face of one row faces the ventral
face of the other row—just as the little choir-boys on the Gospel side
of a chancel face the little choir-boys on the Epistle side, but much
nearer together—and that their heads are all directed towards the
corrugated ridge.
They are at first quite white, but with large black eyes, and it
has often struck me how surprised they must be when they awake
to consciousness and find themselves staring at a brother or
sister cockroach just opposite, of whom they have had hitherto no
consciousness. The ripe embryos secrete some fluid, probably saliva,
which dissolves the ridge, and it is through this dissolved or softened
ridge that they ultimately make their way into the outer world.
Young cockroaches are very active, running about and seeking everywhere
for any food of a starchy nature. They are, in fact, miniatures of
their parents, for a cockroach, like many of the primitive insects, has
a direct development, and there are no such stages as caterpillar and
pupa in their life-history.
But, like other insects, cockroaches change their skin from time to
time, and they lose little time before beginning this ecdysis, for
they first cast their cuticle immediately after escaping from the
egg-capsule. The second ecdysis is four weeks later, and the third at
the end of the first year, and after this time they moult annually. At
the seventh moult, when the animal is now four years old, it assumes
the form of the perfect insect, and is capable of reproduction. The
later moults fall in the summer time, and so does fertilisation and
oviposition. Male cockroaches may be distinguished from the females by
their well-developed wings and wing-covers. They stand higher on their
legs than do the females, whose abdomens often trail upon the ground.
In spite of the noxious secretion of their abdominal glands there are
creatures who habitually feed on cockroaches—hedgehogs, for instance,
are frequently imported into our houses to check these pests. Rats,
cats, polecats, frogs, and wasps have been known to eat them, and some
few of the digging-wasps lay them down in their larders for the use
of their progeny. Some birds will also tackle them. But even the most
devoted friend of cockroaches can find little to say in their favour,
except that they are currently reported to form the basis of the
flavouring of a very popular sauce; but even wild cockroaches will not
drag from me what the name of that particular sauce is.
CHAPTER II
COCKROACHES (_Periplaneta_)
PART II
In Russia the small Asiatic cockroach (_P. orientalis_) has everywhere
driven before it its greater congener (_P. germanica_).
(DARWIN, _Origin of Species_.)
Cockroaches do a very considerable amount of damage by consuming
food-supplies. But they do not stop at food-supplies: woollen clothing,
newspapers—not a really great loss—blacking, ink, leather, and even
emery-paper, are all to their taste, and, being of an economical frame
of mind, they devour their own cast skins and the dead bodies of their
relatives. The late Professor Moseley recorded how on one occasion,
when on the circumnavigating tour of H.M.S. _Challenger_, a number of
cockroaches took up their abode in his cabin and devoured parts of his
boots, ‘nibbling off all the margins of leather projecting beyond the
seams on the upper leathers.’ He further records:—
One huge winged cockroach baffled me in my attempts to get rid of
him for a long time. I could not discover his retreat. At night he
came out and rested on my book-shelf at the foot of my bed, swaying
his antennae to and fro, and watching me closely. If I reached out
my hand from bed to get a stick, or raised my book to throw it at
him, he dropped at once on the deck, and was forthwith out of harm’s
way. He bothered me much, because, when my light was out, he had a
familiar habit of coming to sip the moisture from my face and lips,
which was decidedly unpleasant, and awoke me often from a doze. I
believe it was with this object that he watched me before I went to
sleep. I often had a shot at him with a book or other missile as he
sat on the book-shelf, but he always dodged and escaped. His quickness
and agility astonished me. At last I triumphed by adopting the advice
of Captain Maclear and shooting him with a pellet of paper from my
air-gun, a mode of attack for which he was evidently unprepared.
It is on record that cargoes of cheeses have been destroyed by
cockroaches on ships. Not only did they devour great quantities of each
cheese, but they defiled every one of them with their very tenacious
fluid which has, as we have noted above, a most disgusting smell. This
the cockroaches poured out from their stink-glands, making the cheeses
of no commercial value.
When a cockroach casts its skin a median longitudinal slit appears
on the back of the thorax, and through this slit the insect slowly
emerges. With much labour and difficulty it squeezes its body through
and pulls one limb after another from its old integument, until at last
even the long whip-like antennae are completely withdrawn. Certain
portions of its inner anatomy—such as the lining of parts of the
breathing-tubes, or tracheae—are also withdrawn. Should the discarded
skin not be eaten by the emergent insect, it remains on the floor, and
might easily be mistaken for a sedentary cockroach but for the fact
that live cockroaches never are sedentary.
[Illustration: FIG. 6.—Cast skin of older nymph (pupa). × 2½. (From
Miall and Denny.)]
[Illustration: FIG. 7.—Nymph (in last larval stage) escaping from old
skin. Magnified. (From Miall and Denny.)]
The incomplete metamorphosis, the generalised character of the nervures
of the hind wings, the complete separation of the three thoracic
segments (or rather their want of that fusion so conspicuous in the
higher insects—the flies and the bees) and the undifferentiated
condition of the mouth parts—all point to the insect being of a
primitive type. But there is no doubt that, whether a primitive
insect or not, the cockroach is a very successful one; it is an
_arriviste_—as ‘our lively friend, the Gaul,’ to quote Mr. Micawber,
would say—probably owing to its attaching itself in all cases, and
with unvaried devotion to the habitation of men. Not popular with
humanity, it nevertheless ceaselessly extends its domain by slowly yet
surely entering into new and hitherto unconquered human habitations.
In spite of insect-traps and vermin-killers, it is extremely difficult
to eradicate from a house when once it is well established. It has, in
fact, gradually dislodged in most places in Great Britain and Ireland
the old domestic house-cricket. For in spite of its irritating, and to
some people quite maddening, ticking, the ‘cricket-on-the-hearth’ has
somehow established itself as a household pet, and one that has won not
only our respect but our affection. So curious is our psychology.
The cockroach has many enemies, and the genus _Sphex_ (or _Chlorion_)
may be seen hunting about here and there, up and down the road-side
and gardens, searching for its favourite prey. It spies out a
cockroach, which appears to know intuitively that there is danger at
hand, for it shows symptoms of great fright, and seems so confused
that it cannot run away. The _Chlorion_ pounces upon the insect,
clasps it with its mandibles between the head and the corselet, and
stabs it in the body with the sting. Then it flies off for a little
distance, and awaits the effects of the poison thus introduced; and
when the convulsions of the victim have ceased, the clever little
insect seizes its stupefied prey, and drags the heavy burden with
great efforts to its nest. Usually the opening of the cavity is so
narrow that the cockroach cannot be got in, for its legs and wings
stick out and prevent its introduction. But the _Chlorion_ sets to
work and cuts off the legs and the wings, and having thus lessened
the difficulty, it strives hard to push the body into the hole; but
as this plan usually fails, the hymenopteron enters first of all,
seizes the cockroach with its mandibles, and drags it in with all its
force. As the integuments of the _Blatta_ are more or less soft and
flexible, the great insect is at last forced into the gallery, where
it never could have been expected to have entered. Such proceedings on
the part of the _Chlorion_ almost verge upon the domain of reason; and
it is difficult to explain them by the notion of that very indefinite
quality called instinct, for the manœuvres vary according to the
circumstances, and there appears to be an intelligent method of
overcoming every difficulty.[1]
Apart from animals which eat it, there are a number of parasites
which infest it, beginning with the parasitic beetle _Symbius
blattarum_, whose wingless females attach themselves to the bodies
of the cockroaches and feed upon their tissues. Then occasionally a
round-worm, _Filaria rhytipleurites_, whose sexual stage is passed
in the rat, is found in its larval stage in the fat bodies of the
cockroach.
Two years ago Dr. C. Conyers Morrell undertook some investigations
and observations as to what part, if any, cockroaches played in the
dissemination of pathogenic microbes, his object being, as he says,
‘first to ascertain what bacilli belonging to the colon group are
likely to be conveyed to food and milk by this insect, and secondly
to find whether known bacteria and moulds can be transmitted by the
faeces.’ Dr. Conyers Morrell’s experiments were conducted on one of the
Union Castle liners sailing to South Africa, and the insects which were
investigated were collected only from the larder or passages adjacent
to the kitchens; in no case were they taken from lavatories or from
staterooms. The general condition of the ship, which was almost new,
was one of exceptional cleanliness, and thus afforded good conditions
for the experiments. Dr. Morrell was of opinion that there was little
danger except by contamination from the faeces of the infected insect.
[1] _The Transformation of Insects_, by P. M. Duncan. London: Cassell,
Petter, Galpin and Co., 1882.
One of his first experiments was to prove that should cockroaches
fall into the dough which was being baked for bread the heat of the
baking entirely destroyed the bacilli that were in the alimentary canal
of the insect. With regard to infection with the colon bacillus, he
kept an infected insect under the best antiseptic conditions he could
compass until it had passed some undigested food. Of this undigested
food an emulsion was prepared, and cultures were made from it on
bile-salt medium and in litmus-milk. Afterwards special cultures were
made in gelatine and peptone solutions. Incubation was conducted in
all cases at 37° C., and cultures were made from seventeen specimens.
Five of these produced colonies of bacilli on the bile-salt medium,
with sub-culture results as follows: Four produced acidity and
clotting of milk, acid, and gas in glucose, lactose, and saccharose,
and production of indol. But the bacilli did not liquefy gelatine,
and were Gram-negative. One specimen produced gas in glucose and
lactose, and liquefied gelatine and coagulated milk. The former in its
reaction corresponded to the _Bacillus lactis aërogenes_, the latter to
_Bacillus cloacae_. In five cases greenish moulds of the _Aspergillus_
variety were found after inoculating litmus-milk.
Cockroaches will devour human sputum with avidity, and are frequently
to be found in spittoons (or, as the more delicately minded American
calls them, ‘cuspidors’[2]), and it is interesting to know that after
feeding the insects on infected sputum from a tuberculous patient, the
tubercle bacilli are found in the faeces within twenty-four hours; two
specimens which had been fed on staphylococci showed these pathogenic
organisms in their faeces and in the cultures on agar-agar, which were
obtained from their dejecta.
I have quoted largely from this important paper, and now propose
to quote a good deal more, and thus I append Dr. Conyers Morrell’s
conclusion of the important experiments he conducted on the Union
Castle liner.
[2] From the Portuguese ‘cuspidor.’ Cf. the Latin ‘conspuere.’
The foregoing experiments, though insufficient in number to afford a
basis for working out percentage results, are, I think, of some value,
in that they prove the following facts:—
The common cockroach is able by contamination with its faeces (1) to
bring about the souring of milk; (2) to infect food and milk with
intestinal bacilli; (3) to transmit the tubercle bacillus; (4) to
disseminate pathogenic staphylococci; (5) to transmit from place to
place destructive moulds.
These facts, taken in conjunction with the life-habits of the insect,
lead to the conclusion that the cockroach is able to and may possibly
play a small part in the dissemination of tuberculosis, and in
the transmission of pyogenic organisms; that the insect is in all
probability an active agent in the souring of milk kept in kitchens
and larders; and that it is undoubtedly a very important factor in
the distribution of moulds to food and to numerous other articles,
especially when they are kept in dark cupboards and cellars where
cockroaches abound. The distribution and numbers of the cockroach are
rapidly increasing, and unless preventive measures are adopted the
insect is likely in the course of time to become a very troublesome and
possibly a very dangerous domestic pest.[3]
[3] _British Medical Journal_, 1911, ii. 1531.
CHAPTER III
THE BOT- OR WARBLE-FLY (_Hypoderma_)
Apropos de bottes.—(REYNARD.)
Britain wants many materials in this war, and as long as our back
door is open we are getting them. Petrol, rubber, zinc, copper,
molybdenum, vanadium, thorium, nickel, saltpetre, wool, cotton,
are all coming to us in greater—immeasurably greater—quantities
than those in which they can filter through neutral countries into
Germany. These things count. The shortage of leeches in Great Britain,
on which I have already dwelt, is negligible, and is entirely
over-balanced by the really serious shortage of sausage-skins in
middle Europe. I am told that our meat-salesmen at Smithfield
were offered an incredible advance on the normal rate for these
products—so-very-necessary-and-under-no-circumstances-to-be-done
-without-with-casements—but the meat-salesmen at Smithfield were
patriots. In their dire extremity the Germans have been trying to make
them of cellulose.
Amongst the things both combatants most want is leather. One of the
most impressive efforts we non-combatants have been watching, since
August 1914, is an army growing, near us and next us, with apparently
an unlimited supply of leather belts, leather trappings, leather
saddlery—leather harness for man and beast. Yet they tell me that
the price of leather since the War began has appreciated by 140 per
cent. This may be so; but, as Joseph Finsbury remarked in ‘The Wrong
Box,’ ‘there is nothing in the whole field of commerce more surprising
than the fluctuations of the leather market. Its sensitiveness may
be described as morbid.’ But Joseph was no business-man, and kept in
the background of the office a capable Scot who was understood to
have a certain talent for book-keeping. Readers of Stevenson will
remember that nobody had ever made money out of Finsbury Brothers,
Leather-merchants, except the capable Scot who retired (after his
discharge) to the neighbourhood of Banff, and built a castle with his
profits. There are still many capable Scots about, and this may, to
some extent, account for the present price of Sam Browne belts.
There must have been well over 150,000 Sam Browne belts made since the
War began. A widespread belief—at any rate, amongst the junior members
of the Army—is that Sam Browne was an American; possibly some slight
confusion existed in their dear young minds between the inventor of the
belt and John Brown whose ‘body lies,’ &c. The inventor of this useful
cincture was, however, Sir Samuel James Browne (1824-1901), G.C.B.,
K.C.S.I., the well-known Indian fighter, who lost an arm, and gained a
V.C. by his gallantry during the Mutiny. He was for a time the military
member of the Governor-General’s Council, and he commanded the first
division of the Peshawar Field Force during the Afghan War of 1878-9.
The 22nd Regiment in the Indian Army, a frontier force, is known as Sam
Browne’s Cavalry.
The belt was first used unofficially, but it gradually found favour
with the authorities, and it is mentioned officially in the regulations
drawn up for the Straits Settlements in 1891, and for Egypt and West
Africa in 1894. It was only on April 24, 1900, that the pattern was
‘sealed,’ and adopted as a general item of equipment for all officers
on Active Service.
Anything that seriously destroys the continuity of the integument of
our oxen, which interferes with the ‘wholeness’ of the hide which is
the basis of leather, clearly affects—and affects detrimentally—an
important munition of war. The bot- or warble-fly does this. But
it does more: its attacks materially lessen the value of the beef
which potentially lies beneath the hide, and thus in a double sense
the warble-fly is the enemy of man whether he be soldier or sailor.
Further, its attacks seriously lessen the milk-supply of the country.
Amongst the numerous families into which the true flies (DIPTERA) are
divided, none are more harmful to human enterprise than that of the
_OESTRIDAE_, or bot-flies, inasmuch as every single species and every
single member of this family passes its larval stage within the tissues
of some vertebrate host, and frequently in those of domesticated
cattle; sometimes even in man himself. One of the commonest genera
of this family of flies is _Hypoderma_, which is represented in our
islands, and in many other parts of the world where domesticated cattle
are reared, by two species—_H. bovis_ and _H. lineatum_, both commonly
known as bot- or warble-flies.
The harm caused by these larvae, living as they do in the tissues of
the body, beneath the skin, by piercing holes through the integument or
skin, whereby they make their exit from the ‘warble’ or subcutaneous
tumour in which they have passed their latest larval stage, is almost
incalculable.
[Illustration: FIG. 8.—_a_, _Hypoderma bovis_; _b_, maggot of _H.
bovis_; _c_, egg of _H. bovis_; _d_, puparium of _H. bovis_; _e_,
egg of _H. lineatum_; _f_, maggot of _H. lineatum_; _g_, _Hypoderma
lineatum_. All the figures are magnified. (From F. V. Theobald’s
_Second Report on Economic Zoology_, British Museum, 1904.)]
Miss Ormerod, who for so many years kept alight the lamp of economic
entomology in England, published some statistics on this subject
towards the end of the last century. In 1888, out of slightly over
100,000 hides dealt with in the Newcastle cattle and skin market,
60,000 were ‘warbled,’ and the loss to the trade amounted to £15,000.
The same year at Nottingham 8500 out of 35,000 hides were largely
spoiled; at Manchester 83,500 out of 250,000 suffered from the same
cause: the losses in these towns being estimated for the year in
question at about £2000 and £17,000 respectively. Taking the average
from all sources in England, Miss Ormerod estimated the fall in value
at from 5s. to 6s. on every warbled hide. The most riddled hides—that
is, those with the most punctures—come to the sale-room during April
and May, but the trouble extends from February to September.
There is also the loss caused by the warble to the butcher—and through
the butcher to the Army Service Corps. The presence of the fly-larva,
which is quite a large creature, induces chronic inflammation in the
tissues, and a state of things known to the trade as ‘licked beef,’
and unless the meat-salesman cuts away the affected parts the meat is
unsaleable in the market, or greatly depreciated in value. The average
loss to the butcher on a warbled carcass is estimated at 6_s._ 8_d._
Finally there is a loss to the stock-raiser and dairy farmer. We shall
have occasion later to refer to the curious psychological effect the
warble-fly has upon the cattle, causing them to ‘gad’ or stampede
in wild gallops, which interferes with fattening, deteriorates the
milk-supply, and is especially injurious to cows with calf. Mr. Imms,
in his most useful summary of the warble-fly, tells us that the loss
due to _H. lineatum_ in America is calculated at 28 per cent. of their
total value of all the cattle in the States. Some authorities place
the total loss to the agricultural community in England at £2,000,000,
others at £7,000,000, a year, whilst others estimate that the loss
amounts to about £1 sterling on every head of horned cattle.
Curiously enough, the fly itself is rarely seen, and still more rarely
taken. Mr. Imms records only two specimens of _H. bovis_ in the
collections of the British Museum, and but fifteen of _H. lineatum_. A
similar scarcity of imagos in public collections obtains on the other
side of the Atlantic, where for many years the last-named species
was alone recognised. Two years ago, however, Dr. Hadwen, working in
Canada, established the widespread existence of _H. bovis_ in the
Dominion; almost certainly it also occurs in the States; but Dr.
Hadwen had to send to Dublin for specimens with which to confirm his
find. None existed in the collections in Ottawa, and a ‘request for a
specimen ... from the Bureau of Entomology at Washington, D.C., could
not be granted owing to a scarcity of specimen’! These statements are
interesting, since at present the tanneries of Canada are working night
and day to help our shortage in leather at home.
_H. bovis_ measures ⅝ in. in length, _H. lineatum_, somewhat less
robust, ½ in.; the hairy covering of the last named is of a foxy red
at the tail end, while that of _H. bovis_ is yellow, both at the tail
end and towards the front of the body. The flies are most abundant
during July and August, though they are believed to occur throughout
the summer. At Athenry (co. Galway) _H. lineatum_ is common by the
middle of May. They fly very rapidly, and are difficult to follow with
the eye. They rejoice in warm, sunny weather, and remain in retirement
during cold or cloudy days. Hadwen describes the egg-laying by the
female ‘as a sort of frenzied process, the fly striking’ with its
ovipositor twenty or thirty times rapidly, then leaving the animal for
fifteen minutes or so, when the process was repeated. The eggs are
attached one at a time to the hairs of the cattle and very close to the
base of each hair, not near the tip, where the horse bot-fly deposits
its ova. The eggs of _H. bovis_ are scattered and isolated; those of
_H. lineatum_ are arranged in rows of some seven or more half-way up
the hair and are contiguous. The favourite region for placing the
eggs is on the hock and on the back of the knee, or on the thighs and
flanks, and hence the American cowboys call the insect the ‘heel-fly.’
Undoubtedly by standing with their legs in water the herd is delivered
from the pest—at any rate, for the time.
[Illustration: FIG. 9.—Eggs of _H. lineatum_, attached to hair of cow.
Five of the eggs are hatched and six unhatched. Magnified 15 times.
(From Carpenter, Hewitt, and Reddin, _Journ. Dept. Agric. Ireland_,
xv., 1914.)]
The eggs are large, 1·25 mm. in length, and enclosed in a whitish
shell, which is prolonged behind into a brownish foot, and this foot,
which exudes some sticky excretion, adheres to the ruminant’s hairs.
The foot of the egg-shell, in fact, consists of two lobes or valves,
which clasp the hair between their sticky inner surfaces.
[Illustration: FIG. 10.—Eggs of _H. bovis_ attached to hairs. Note
attachment near base. Slightly enlarged. (From Hadwen.)]
Within the egg the youngest of the four larval stages is maturing. When
hatched it is less than 1 mm. long, but it is ‘a terror for its size,’
being armed with a formidable spine and two hooks in the mouth, and
with rows of strong spines on all the body-segments. Later, we find
a second stage, very much smoother and less spiny than the first and
this lies within the tissues of the host, embedded in its muscles and
membranes, notably in the submucous coat of the gullet; and now the
question confronts us, which once confronted George III apropos of
the apple in the apple dumpling, ‘How the devil did it get in?’ There
seems to be with _Hypoderma_ but two possible modes of entrance into
the body of its host—that is, domesticated cattle: (1) The eggs, or the
newly hatched larvae, are licked up by the tongue, as are the eggs of
the horse bot-fly—and this might be held to explain the not infrequent
occurrence of the second larval stage in the walls of the oesophagus;
or (2) the larvae bore their way directly through the skin. From
experiments carried on for several years which show that cattle unable
to lick themselves are not protected from warbles, Professor G. H.
Carpenter of the Royal College of Science, Dublin, concluded that the
larvae do not enter by the mouth. During the summer of 1914, he and his
able assistant, the late Mr. T. R. Hewitt, definitely proved that ‘the
newly hatched maggot does bore through the skin of cattle’; probably
after an ecdysis they find their way to the submucous coat and muscles
of the gullet, and here for a while they rest. I quote from the account
of Carpenter and Hewitt some of their most crucial experiments carried
out at the Athenry and Ballyhaise Stations of the Irish Department of
Agriculture:—
In July 1914, twenty-four maggots were hatched in the incubator, and
some of these were used for observations as to behaviour when placed
on a calf’s body. Glaser, in 1913, had tried to carry out observations
of this kind by placing maggots on a shaved portion of a calf’s skin;
he found that they made no effort to bore through. Instead of being
shaved, a small patch of the shoulder of one of the Ballyhaise calves
was clipped, so as to have the conditions as normal as possible, when
newly hatched maggots of _H. bovis_ were placed on it. Immediately
they started crawling down the clipped hairs to the skin, and, as soon
as they reached the surface, they began to burrow. On account of their
small size it is hard to discern them, but by carefully watching
through a lens it was seen that they enter perpendicularly to the
surface, evidently cutting into the epidermis with their mouth-hooks
and occasionally bending their bodies. Mr. R. G. Whelan, A.R.C.Sc.I.,
Superintendent of the Ballyhaise Agricultural Station, kindly helped
in the observations and confirmed them. Six hours after being placed
on the calf, the maggots disappeared completely. Next morning the
spots where they had entered were marked by little pimples, like
those of the Athenry animals, easily to be seen with the naked eye.
These increased slightly in size, but soon healed up, and in less
than a week not a trace of the maggots’ entrances could be found. The
boring-in of the maggots seemed at first to cause the calf a little
pain, but the symptoms of discomfort soon passed away.
We have still to find out what happens to the first-stage larva after
it has bored into the skin and how far it travels before it undergoes
its first moult. Gläser found that some eggs of _H. lineatum_ laid
on his trousers hatched, and that a maggot bored right through into
his own skin. From symptoms of swelling and pain in various regions
he concluded that this maggot travelled to his gullet, and he finally
extracted it (in the second stage) from his mouth.[4]
[Illustration: FIG. 11.—Entrance hole of _H. lineatum_ maggot into
the skin of a cow. The hairs around the hole have been clipped short.
The white incrustation is due to a discharge from the hole, which has
hardened. Magnified 12 times. (From Carpenter, Hewitt, and Reddin,
_Journ. Dept. Agric., Ireland_, xv., 1914.)]
Perhaps in the first stage they may be carried by the blood stream.
They seem in their second larval stage to wander freely through the
tissues, especially through the muscular tissues, of the body of
their host—usually working upwards, and not infrequently reaching the
neighbourhood of the vertebral column before taking up—still in the
second larval stage—their final position, where their presence gives
rise to the ‘warbles,’ or subcutaneous cysts or tumours, in which the
third and fourth larval stages are passed.
[4] _The Irish Naturalist_, October 1914.
It seems odd that an insect pest, which so seriously affects our supply
of leather, of meat, and of milk, should have been studied for over a
century and yet conceal its chief secret from man. But the problem is
much more difficult than the layman thinks.
Whatever be the route the maggot travels through the body of the calf
or cow, by the spring the fourth larval stage—when it is about an inch
long, and perhaps half as much in breadth—is reached in the ‘warble’
or cyst, under the skin. Here, nourished by the products of the
inflammation it sets up, and breathing by two spiracles at the hinder
end of its body, which are directed to the opening of the ‘warble’
which it has pierced through the skin, the larva rests until one fine
morning it pushes its way, aided by its stout bristles, through the
opening and tumbles into the outer world.
Apparently it does not think much of its new surroundings, for it loses
no time in hiding under some clod of earth or stone or crevice in the
soil, and straightway turns into a dark brown pupa or chrysalis. This
stage lasts three to four weeks, and then the perfect fly emerges, and
will soon be ready to lay her eggs on some new victim.
[Illustration: FIG. 12.—Cow being chased by fly. Note terrified look of
eyes. (From Hadwen.)]
As a rule it is the yearlings who suffer most, and then the
two-year-olds; the older cattle being comparatively immune. The
inexplicable terror which the warble-fly induces in its victims is
testified to on all hands, but has never been adequately explained.
_Hypoderma_ does not bite, neither does it sting. Many other
blood-sucking insects, whose puncture must involve some pain, are
tolerated by cattle with a flick of the tail, or are frightened off by
a gesture of the head; but the presence of the warble-fly induces a
mysterious fear which rapidly spreads through a herd, and results in
a general stampede—often referred to by cattle-breeders as the ‘gad.’
This terror communicates itself even to the ‘stalled ox,’ and cattle
confined within cowsheds show symptoms of extraordinary unrest when the
fly is abroad amongst their kin in the pastures. The resulting evils
are, of course, far graver in the unlimited prairies of the West—the
great cattle-breeding districts of the United States and Canada—than in
our carefully hedged or fenced meadows. A great many ‘dips,’ ointments,
and chemical solutions have been recommended for the prevention of
the grubs in cattle, but none have proved entirely satisfactory. The
tedious method of removing the grub from the tumour is the only safe
one. This can be done by the mere pressure of the fingers when the
grub is nearly mature and ready to leave its host, or by the use of
small forceps should the grub be young and recalcitrant. Once removed
the grub should be immediately destroyed, and some such antiseptic as
coal-tar applied to the lips of the vacated tumour.
CHAPTER IV
THE MOSQUITO (_Anopheles maculipennis_)
PART I
Where the water is stopped in a stagnant pond,
Danced over by the midge.
(R. BROWNING, _By the Fireside_.)
There is no zoological distinction between a mosquito, a gnat, or
a midge. But, as a matter of convenience, we might confine the
term ‘gnat’ to the genus _Culex_, the term ‘mosquito’ to the genus
_Anopheles_, and the term ‘midge’ to the genus _Ceratopogon_ and its
congeners, whose collocation with the naked knees of the Highlander is
said to have given rise to the ‘Highland Fling.’
There is no doubt about it that both the mosquito and the gnat are
extraordinarily beautiful insects. This fact, however, has been veiled
from the public partly owing to their small size and more especially
because of their irritating bite, which causes the sufferer to kill
a mosquito at sight rather than examine its fairy-like beauty or its
fascinating dances in the air, far surpassing in grace and agility
anything seen in the Russian ballet. But biting is the dominating note
of a mosquito, and we may as well consider, to begin with, how it bites.
If we examine the head of a mosquito we shall find that it is shaped
like a circular cushion bearing two enormous eyes—so large that in the
male they touch above the forehead and almost meet below the chin. Each
eye consists of hundreds of facets of a brilliant green hue, set in
a darkish background, like emeralds arranged on a black surface. The
head also bears a quantity of hairs and flattened scales whose number,
shape, and arrangement are of considerable systematic value.
The following are the appendages of the head:—
1. A pair of antennae, which are markedly different in the two sexes.
2. A pair of mandibles. These are absent in the male.
3. A pair of first maxillae, each of which has a jointed tactile palp.
4. A pair of second maxillae which have fused together to form a deeply
grooved soft process in which the other appendages lie.
Beside these four pairs of appendages, which are in reality modified
limbs, there are two median processes, which project one from the
top, the other from the bottom, of the mouth, like elongated and
hardened upper and lower lips. These are the median labrum above—a
deeply grooved structure whose edges approximate and almost touch, thus
forming a tube along which the blood of the victim is sucked. Lastly,
there is the hypopharynx—sometimes termed the tongue—a median structure
a double-edged sword, rising from the bottom of the mouth, and it is
this that is the cause of all the trouble.
[Illustration: FIG. 13.—Side view of the head of a female _Anopheles
maculipennis_ (magnification about 20), with the various mouth
parts separated, but in the relative position in which they lie
when enclosed in the groove of the labium. This figure shows the
characteristic cephalic scales, _a_, Antennae; _cs_, cephalic scales;
_cl_, clypeus; _lxe_, labrum + epipharynx; _mn_, mandible; _hp_,
hypopharynx; _mx_, first maxilla; _li_, labium; _mp_, maxillary palps.
(From Nuttall and Shipley.)]
[Illustration: FIG. 14.—Transverse section through the middle of the
proboscis of a female _Anopheles maculipennis_, showing the relative
position of the parts when at rest. Two tracheae and two pairs of
extensor and flexor muscles are seen in the labrum. _lxe_, Labrum +
epipharynx; _tr_, trachea; _mus_, muscles; _hp_, hypopharynx; _sal_,
salivary duct; _mx_, first maxilla; _mn_, mandible. (From Nuttall and
Shipley.)]
A glance at Fig. 13 will show how these various mouth appendages
can by a skilful use of dissecting needles be separated out, but in
nature they are all packed together in a case; the arrangement in the
case is shown by Fig. 14, which represents a transverse section of
the proboscis. The term ‘proboscis’ is given to the totality of all
these structures taken and packed together. With the exception of the
labium and of the tactile maxillary palps all the mouth appendages
lance into the skin. The proboscis of the male is, however, too weak
to pierce the human integument, and it is the female which does all
the damage. When a mosquito is going to bite, she alights so gently
that her approach is unperceived, and she proceeds to thrust her
arsenal of weapons into the epidermis of her victim almost unfelt; the
feeling comes later. These weapons are all guided, by the forked end
of the softened labium, just as one’s finger-tips guide the end of
a billiard-cue. These ‘mouth parts’ are exceedingly fine, extremely
sharp-edged structures, whose consistency is about that of whalebone,
and both the mandibles and the maxillae have a toothed, serrated edge
(Fig. 15). They are partly pushed in by muscles in the head, partly,
I think, by the lowering of the body, and they sink slowly and surely
into the flesh with as much ease as a paper-knife will penetrate a
cream-cheese. But as they sink deeper and deeper into the integument
the body of the mosquito approaches nearer and nearer to the skin of
the victim, and the labium is pressed farther and farther backwards
until at the end of a satisfactory puncture the distal and proximal
parts of the labium are parallel and touching.
[Illustration: FIG. 15.—A side view of the labellae and
piercing-organs of the proboscis of a female _Anopheles maculipennis_,
dissected out to show the tips of the mandibles, maxillae, and labrum
+ epipharynx. The hypopharynx is not shown, _li_, Labium; _lxe_,
labrum + epipharynx; _mx_, first maxilla; _mn_, mandible; _la_,
labellae. (From Nuttall and Shipley.)]
It is rather an interesting point that the labium does not enter the
skin, because the larvae of certain _Filarias_—one of which produces
elephantiasis in man, and the other severe heart trouble in the dog—are
found in pairs—probably a male and a female—in the labia of mosquitos.
How exactly these nematode larvae leave the labium of the mosquito, and
enter the body of the man and the dog, has not definitely, I believe,
been cleared up; but that they do enter the human and the canine skin
seems certain.
We have mentioned that the labrum is a grooved tube with its edges
practically in proximity, and it is up this tube that the blood of the
bitten is sucked by the well-known suctorial pharynx which occupies so
large a part of the interior of the head of a mosquito. Much the most
dangerous weapon of the whole armoury, however, is the hypopharynx.
This is shaped like a double-edged sword with a very minute groove
running down the centre; this groove is so minute that Professor
Nuttall and I and others for some time took it to be a closed tube.
It receives at its base the products of the salivary glands of the
mosquito, and it is these products which contain the organisms which
cause malaria—a disease which has probably caused more trouble and has
played a greater part in the history of the world than any other malady
to which humanity is heir. Down this minute, microscopic groove has
flowed the fluid which has closed the continent of Africa for countless
centuries to civilisation, and which has played a dominating part in
destroying the civilisations of ancient Greece and of Rome.
When the adult mosquitos (the imagines) leave their pupa-cases they are
unable to pierce the human skin until the mouth parts have hardened,
and this takes at least six hours. In England they can undoubtedly
feed twenty-four hours after leaving the pupa-case. When feeding,
both the sensory antennae and the tactile maxillary palps are thrust
forward at right angles to the proboscis. They thus test the place
where the two-lobed extremity of the labium will guide the battery of
stylets into the substance they are feeding on. The female is much more
voracious than the male, which, as we have mentioned above, cannot
pierce the human integument, and has to be content with a vegetarian
diet. Sometimes the effort even of the female mosquito to insert its
proboscis is fruitless, and we have watched a mosquito attempt four
times to pierce the skin before it drew blood. If undisturbed during
the meal the suctorial repast may last some two or three and a half
minutes. So greedy at times is the mosquito that she resembles Baron
Munchausen’s horse after the adventure with the portcullis—what is
flowing in at one end is flowing out at the other. In fact, as Dr.
Johnson said of the boys at a school ‘where discipline was maintained
without recourse to corporal punishment,’ ‘But, sir, what they gain
at one end they lose at the other!’ After the process of biting, of
sinking-in of the piercing needles, is complete, the proboscis is
withdrawn, and to do this the mosquito braces herself on her legs and
raises her body.
Another curious feature about the head of _Anopheles_ is that it is
pierced by two chitinous, symmetrical tunnels—tubes which are open at
each end with trumpet-shaped orifices. The use of these is probably to
act as a stay or strut to strengthen the chitinous exoskeleton of the
head; but these queer galleries or tubes also to some extent act as
attachments for muscles.
The antennae vary very much in the two sexes. In the female there
are fifteen segments, each bearing a ring of hairs, but of small and
disproportionate size, whereas in the male the bushy character of the
hairs is conspicuous even to the naked eye. In fact, it is the easiest
criterion for judging the sex of the insect. At the base of the first
joint of the male antenna is a deep cup-shaped structure packed with
sense organs, and containing a large nerve ganglion. There are sixteen
segments in the whole antenna, one more than in the female. The hairs
are capable of movement, and as a rule are kept closed on the shaft of
the antenna whilst not in use; when evening comes on they are spread
out. There seems little doubt that these organs are auditory and help
the male in searching for the female.
The beautiful transparent wings of the mosquito are beset with minute
spikes, which serve to break up the light and to give rise to the
many-coloured iridescence of the creature’s wings. The posterior border
of the wing bears rows of beautifully graded scales. These add much
to the symmetry and beauty of the whole structure. Just behind it are
two balancers or halteres—a name derived from the Greek word ἁλτῆρες,
meaning a kind of dumb-bells which athletes used in the stadium when
jumping. These so-called balancers project outwards and backwards from
the body when the wings are in a position of flight.
A curious distinction between the _Culex_ and _Anopheles_ is in regard
to the position assumed by the insects when they rest. In _Anopheles_
the proboscis and body are almost in one line, and the axis of the
body is at an angle with the surface upon which it rests. _Culex_, on
the other hand, has its proboscis at a slight angle with its body, and
its body is almost parallel to the surface upon which it is perching.
_Culex_ has a much more hump-backed appearance than _Anopheles_, and
its legs are considerably shorter and stouter. The insect generally
rests upon four out of six legs; in the former case the hinder pair are
held out and curved upwards. The hind legs not infrequently serve as a
test for food. When feeding upon sweetened milk or fruit, the moment
the hind leg touches the fluid or juice the insect will wheel round and
at once begin to feed.
_Anopheles maculipennis_ is very widely distributed, and it has been
recorded from most parts of North America and Europe, and from many
parts of Asia. Probably the species is much more widely distributed
than we have any record, but individuals do not wander very far,
of their own accord, from the breeding-places, though they may be
dispersed by the wind. Cases are known where they have been blown as
far as ten or even twenty miles; and in camping in Africa it is always
well to keep to the windward of a native village. They are also
carried about by trains, motors, and steamers. They do not indulge in
any such voluntary migratory flights as the locusts, although some
such flights have been from time to time recorded, but these ‘swarms’
are probably due to a high wind catching a large number of mosquitos
temporarily associated.
In a joint paper which Professor Nuttall and I wrote some years ago, we
drew attention to a case in which mosquitos came aboard a ship some ten
miles from land, and to another in which a Spanish barque from Rio was
detained in the South Atlantic quarantine station of the United States.
The vessel was so much infested with mosquitos that it was rendered
nearly uninhabitable, and the United States quarantine officer reported
that when the forecastle was opened after fumigation ‘the mosquitos
could be scooped up by hand.’ The master of the barque was positive
that there had been no mosquitos on board until the twenty-second day
out. Howard quotes a letter from a General living in Texas in which he
states he has ‘twice seen flights of _Culicidae_,’ but as the species
and the genus are not given, much of the interest of the statement
evaporates. Generals living in Texas are not invariably remarkable for
meticulous accuracy in recondite scientific matters.
CHAPTER V
THE MOSQUITO (_Anopheles maculipennis_)
PART II
There in a wailful choir the small gnats mourn
Among the river sallows, borne aloft
Or sinking as the light wind lives or dies.
(JOHN KEATS, _To Autumn_.)
The female imago hibernates. Finsch made observations and found it
hibernating on the frozen Siberian tundras, beneath the moss and snow.
Sterling found them in North America when the snow was melting, in
great numbers, and he and his party were subsequently terribly bitten.
There is no doubt that female imagines live throughout the winter, and
they can be found in England, hibernating in cellars, old out-houses,
chicken-houses, or disused farm buildings. These hibernating females
disappear early in May, presumably having laid their eggs. Dr. Thayer
of Baltimore describes these creatures, having found them on the roofs
and walls of barns near New Orleans. Whether the male also hibernates
is doubtful. Grassi says he never found the male of _A. maculipennis_
in the winter, only fertilised females. But as the warm weather sets in
the female generally becomes active and bites, and the native American
Indians consider these elderly and famished females give more annoyance
than at any other stage in the life-cycle of either sex. In the warmer
climate of Southern Italy they not infrequently hibernate in grottos
and caves. At times they occur in such numbers that they can be swept
up. After depositing their eggs the hibernating females probably die.
This usually happens in May.
In the old days we used to collect gnats, keep them in a receptacle
unprovided with any food, and when, after a couple of days, they died
of starvation we wrote poems or essays on the ‘Transitoriness of Life’
and the ‘Evanescence of Time.’
The thin-winged gnats their transient time employ,
Reeling through sunbeams in a dance of joy.
(MRS. NORTON.)
Nowadays, we feed them. Bananas, sweetened milk, pineapple, or almost
any other vegetable juice, is their diet, and in captivity they will
live for weeks. At Cambridge in 1900 (July to August), Professor
Nuttall was successful in keeping females alive on a diet of bananas
and water from two to eight weeks, but it was found essential to keep
the atmosphere fairly moist and the food fresh. Grassi found that he
could only keep _Anopheles_ alive in his laboratory in Rome for a month.
Both _Anopheles_ and _Culex_—at any rate, in captivity—lay their eggs
early in the morning. Apparently the nature of the food has some
effect upon their fertility, certain observers stating that when male
and female are fed on vegetable food alone there is no fertilisation
and no oviposition. A diet of blood evidently assists the female to
lay her eggs, and perhaps to get them fertilised. One of our female
_Anopheles_ laid a batch of 146 eggs, and subsequently laid six more.
But, as a rule, a fertilised female does not lay a second batch unless
she receives a second meal of blood. The eggs are laid two or three
days after the meal. There is also some evidence that a meal of blood
is necessary if fertilisation is to be effected. As Austen says in
_The Report of the Sierra Leone Expedition of the Liverpool School of
Tropical Medicine_:—
The following law is likely to hold good for the _Culicidae_ which
feed on man—at least for the common species; although these gnats can
live indefinitely on fruit, the female requires a meal of blood both
for fertilisation and for the development of the ova. In other words,
the insects need blood for the propagation of their species.
Undoubtedly, if mosquitos ever talk, they would talk like Mr.
Waterbrook, Mrs. Henry Spiker—Hamlet’s aunt—and the ‘simpering
fellow with weak legs’ talked when David Copperfield dined with the
first-named at Ely Place, Holborn. The burden of their song was: ‘Give
us blood.’
But a word of caution must be given here. Most of these deductions are
based upon mosquitos in captivity; whether the same be true of them in
natural conditions is not quite certain. If it be so it is difficult to
see how these countless millions of gnats and mosquitos which dwell in
the barren regions around the polar circle ever keep going.
It very frequently happens in the Animal Kingdom that females are much
more numerous, as well as much larger, than the males.[5] As Kipling
tells us: ‘The female of the species is more deadly than the male,’
but Professor Nuttall and I did not notice that this was the case with
_Anopheles_.
[5] This is a fact I have always tried to conceal from Mrs. Pankhurst;
but, sooner or later, she is bound to find it out.
There is some evidence that the male hatches out earlier than the
female, and that in Southern Europe there may be three or four
generations in the course of the season: the first beginning in April
and the fourth taking place between the middle of September and the
middle of October. After that date no larvae were found. About four
generations also occurred in the neighbourhood of Cambridge, according
to observations of Professor Nuttall.
Kerschbaumer has calculated that if the average number of eggs laid by
a female be 150, the number of the descendants by the fourth generation
would amount to 31 millions. This readily accounts for the fact
that in certain parts of the world they occur in perfectly enormous
numbers, and if it be true that blood is essential for fertilisation
and oviposition, very few of these potential mothers can breed. In
nature they will feed on a great number of vegetable juices—melons,
wild cherry-blossom, bananas, oranges, overripe mangoes; they suck
the ‘juices’ of allied species of insects just when the imago is
issuing from the pupa-case and before their integument is hardened,
or they pierce the soft skin of the cicada, and occasionally attack
the chrysalids of a butterfly. One of the most curious sources of food
are very young trout. The adult insect attacks these _petits poissons
filiformes_, ‘literally sucking out their unsuspective little brains
before they could escape.’ Grassi is doubtful whether the adult males
feed at all. He states that he never found any food in their stomach,
nor has he ever seen a male feed. But Professor Nuttall’s experiments
in Cambridge prove that males were seen repeatedly to feed, and to feed
hungrily, on cherries, dried fruits, dates, and bananas.[6]
[6] Owing to the recent restrictions on imported fruit imposed by the
Government the food of these beautiful little insects will be further
diminished. But what does our Government know or care about insects?
[Illustration: FIG. 16.—View of my arm being sucked by _Anopheles
maculipennis_ (female). (From Nuttall and Shipley.)]
As mentioned before, the proboscis of the male is too weak to pierce
the human integument, but Howard notes that it will suck up water,
molasses, and beer; and Gray, at Santa Lucia, mentions that in that
island _Culex_ had developed a marked fondness for port wine. One
particularly favourite food is rose-buds covered with aphides—probably
due to the sweetened secretion which these insects exude. The feeding
is sometimes very ravenous, so that the insects become distended, the
bright colour of blood, or coloured sap, readily shining through the
joints of their chitinous armour.
The reaction to heat and cold is that common to many insects. During
the winter the imagines become torpid, quiescent, and cease to worry
one. With returning warmth they become lively again, and generally
wake from their winter sleep in a state of considerable hunger. They
are insects which prefer darkness to light, and during the day-time
congregate in caverns and grottos, under the shade of trees and bushes,
beneath bridges, in barns, and so on. As the sun sinks they emerge from
their hiding-places and fly during the night.
Cambon, writing on _A. maculipennis_ found in the Roman Campagna, says
that imagines ‘appear a few minutes after sunset and disappear a few
minutes before sunrise.’ We were able to confirm this at Cambridge. The
insects retired into the shadiest parts of the boxes in which they were
living until the time of sunset, when a loud buzzing was heard, and the
insects promptly fed on the food which they had neglected during the
day. We kept our tame mosquitos in a huge gauze tent, and at night they
invariably accumulated on the side which was illuminated by a lamp.
Such mosquitos as were kept in a glass lamp-chimney, closed with gauze
at each end, invariably flew towards the end which was held towards the
light. People who are experienced with mosquitos sometimes keep the
room in which they are sleeping dark and place a light in an adjoining
room, leaving the door ajar, and thus lure them away. It seems a
curious thing that, while these insects are repelled by the diffused
light of the sun, they are attracted by the more concentrated light of
a lamp or candle, but such is the psychology of _Anopheles_.
It is not perhaps solely the influence of light; it may be the
influence of colour; for light is very rarely entirely colourless. In
the many experiments carried on in Cambridge on the natural history of
the mosquito, _A. maculipennis_, not the least interesting were those
directed to ascertaining the insect’s preference for colour. It had
been noticed by many observers that they frequented dark-coloured areas
rather than light: for instance, note how few mosquitos there are on
the white collar of the gentleman in the Frontispiece compared with the
number on his dark head and coat. Austen had pointed out that in a
room with a dark dado it was on the dado that the mosquitos were found
rather than on the whitened walls above. Buchanan noted that the men
when collecting _Anopheles_ in an Indian hospital found they were to
be most easily got by hanging up a dark coat or two upon the walls. A
white coat they always avoided. The proverbial yellow dog of the West
is much less bitten than the Newfoundland, and persons wearing dark
socks and black shoes are more bitten than those who wear light ones.
Natives, although they suffer less in health having acquired a certain
immunity, are undoubtedly more bitten than the Europeans.
The experiments we carried on at Cambridge were as follows: In the
large gauze cubical tent in which the mosquitos were bred and kept, a
number of pasteboard boxes without lids, measuring 20 by 16 by 10 cm.,
were piled up. The boxes were lined with seventeen different coloured
cloths, and were placed in rows one above another, and the order was
changed each day, so that no question of height from the floor or
better illumination entered into the problem. Counts were made of the
inhabitants of each box on each of seventeen consecutive days, with the
following results:—
Average number
Colour of box of mosquitos
in each box.
Navy blue 108
Dark red 90
Brown (reddish) 81
Scarlet 59
Black 49
Slate grey 31
Dark green (olive) 24
Violet 18
Leaf green 17
Blue 14
Pearl grey 9
Pale green 4
Light blue (forget-me-not) 3
Ochre 2
White 2
Orange 1
Yellow 0
——
Total 512
It will be noted that about the level of the pearl grey there was a
marked drop. Pale green and pale light blue, ochre, white, orange,
and yellow—especially the last two colours—seem positively to repel
the insect. Our khaki-clothed soldiers have other advantages than
invisibility to the foe. This matter is worth pursuing farther, and it
might be possible to design mosquito-traps lined with navy-blue; by
periodically exposing them to chloroform or benzine, or by sweeping
out the contents, considerable numbers of mosquitos might be destroyed.
A dark blue, sticky solution might be even more effective. After
reading this chapter in the _British Medical Journal_, Mr. J. Cropper
of Chepstow wrote to me as follows:—
Seeing your article on Colour Selection by _Anopheles_ reminds
me that I found the dark navy-blue lining of my tent this summer
(in Palestine) extremely attractive to mosquitos, almost entirely
_Anopheles_; and when the sun got hot I always noticed an increase in
their numbers, presumably as they came from the herbage and trees near
by. No one ever slept in the tent, and I never found _Anopheles_ bite
in the day-time.
The best way of ‘downing’ mosquitos is to prevent the imago hatching,
and this, as has been indicated, can be done by killing the larvae and
the pupae, which is effected by brushing oil on the water in which
they live. The petrol or crude mineral oil should be renewed from time
to time as it evaporates. When once the mosquitos are hatched, every
effort should be made to keep them outside dwelling-houses by means of
wire screens, but if that be impracticable mosquito-nets should be used
at nights. Professor Lefroy recommends one with sixteen to eighteen
meshes ‘to the inch.’ They may be driven away from a room by burning
pyrethum powder in it, or vaporising cresol or carbolic acid, but of
course this must only be done when a window is open, through which they
can escape. As regards the human body, mosquitos may to some extent be
kept away by smearing the skin with the various essential oils—such
as eucalyptus oil or lemon-grass oil, &c. Mosquitos not infrequently
bite through the socks, but wearing two pairs of socks instead of one
pair, or inserting paper under the socks, often prevents their reaching
the skin, as the proboscis is not long enough to penetrate two woollen
socks, or strong enough to pierce the paper.
CHAPTER VI
THE MOSQUITO (_Anopheles maculipennis_)
PART III
The tiny-trumpeting gnat can break our dream
When sweetest. (TENNYSON.)
It is now pretty well accepted that the auditory organs of the mosquito
are situated in the antennae. Sixty years ago Johnston of Baltimore
was investigating the hearing-apparatus of a gnat, and came to the
conclusion that—
The animal may judge of the _intensity_ or _distance_ of the source
of sound by the _quantity_ of the impression; of the _pitch_, or
_quality_, by the consonance of particular whorls of stiff hairs,
according to their lengths; and of the _direction_ in which the
modulations travel, by the manner in which they strike upon the
_antennae_, or may be made to meet either _antenna_, in consequence
of an opposite movement of that part. That the male should be endowed
with superior acuteness of the sense of hearing appears from the
fact that he must seek the female for sexual union either in the dim
twilight or in the dark night, when nothing save her sharp humming
noise can serve him as a guide.
[Illustration: FIG. 17.—A, _Anopheles maculipennis_, male, showing
large, feathered antennae. B, Head of female, showing antennae with
feathering little developed. (From Nuttall and Shipley.)]
Johnston also notes that the male mosquito is the more difficult to
catch. The bushy, complicated antennae of the male show that of the
two sexes, with the mosquito, as with man, the male is primarily the
hearer, the one who has to listen.
Another American, Mayer, twenty years later made some interesting
experiments confirming the views held by Johnston. He managed to cement
with shellac a species of _Culex_ on to a glass slide, and, placing
it beneath a low-powered microscope, watched the response of the
antennae to tuning-forks of varying strengths. He found that under the
influence of a fork producing 512 vibrations per second certain hairs
of the antennae vigorously vibrated, whilst others were left unmoved.
He measured the amplitudes of the vibrations of these hairs under the
influence of the sound emitted by various tuning-forks. Different hairs
were seen to vibrate to different notes. Mayer also observed that when
the sound came from a direction in line with the long axis of the
antennary hair vibrations ceased altogether. Hence he argued that the
antennae could register the direction whence the sound came. Observing
the antennae under the microscope, he confirmed the view that the
vibrations ceased when the hairs pointed towards the source of sound,
and on drawing a line in the direction in which the hair pointed, he
found that it always cut within 5° of the position of the source of
sound. He concludes:—
The song of the female vibrates the fibrillae of one of the antennae
more forcibly than those of the other. The insect spreads the angle
between his antennae, and thus, as I have observed, brings the
fibrillae, situated within the angle formed by the antennae, in a
direction approximately parallel to the axis of the body. The mosquito
now turns his body in the direction of that antenna whose fibrils are
most affected, and thus gives greater intensity to the vibrations
of the fibrils of the other antenna. When he has thus brought the
vibrations of the antennae to equality of intensity he has placed his
body in the direction of the radiation of the sound, and he directs
his flight accordingly, and from my experiments it would appear that
he can thus guide himself to within 5° of the direction of the female.
There has always been some divergence of opinion as to how the buzzing
sound to which the male so readily reacts is produced. Howard once
thought that it was due to vibrations of certain chitinous processes
in the large tracheae. Our experiments showed, however, that when the
wing was cut off closer and closer to its origin the sound decreased in
volume, but the note progressively rose. Unlike human beings, the male
at all times emits a higher pitched note than the female, and in both
sexes the note rises after feeding. ‘The greater the meal, the higher
the note.’ This is, however, by no means confined to mosquitos. It is
a matter which any one must have noticed when assisting at a public
dinner or when dining in a college hall.
Three unfed females gave a note of from 240 to 270 vibrations. One
unfed female gave an abnormally low note of about 175 vibrations. Four
other females, which were arranged in the order of the distension of
the abdomen, after food gave notes corresponding to 264-281-297-317
vibrations; whereas three unfed males all gave exactly the same note
corresponding to 880 vibrations. The explanation of the higher note
of the males is probably that their wings are markedly narrower and
shorter than those of the females.
Whilst working at _Anopheles_ the late Mr. Edwin Wilson, the artist who
was drawing our plates, observed at the base of the wing a structure
which may possibly account for the tone which is so characteristic a
feature of the buzzing. The articulation of the wing with the body is
extremely complex. There seems to be a series of structures like minute
knuckle-bones articulated with one another, and at the outer end of the
series are two ribbed rods which may play some part in the production
of the overtones. One is a chitinous bar with some fourteen or fifteen
well-marked ridges. In certain circumstances we consider that the other
toothed rod can rasp across the ridges of the bar below it. As the wing
is raised and lowered it seems probable that the slightly movable rod
would be drawn across the ridged bar.
[Illustration: FIG. 18.—B, Right half of thorax of _Anopheles
maculipennis_, Meig, with base of right wing and right halter,
magnified about 30. A, The same magnified about 5, to show the area
which bears the stridulator. _tb_, The teeth which rasp on the ridges
borne by _bl_; _kn_, papillae on knob; _h_, distal end of halter;
_scl_, chitinous thickenings. (From Shipley and Wilson.)]
We have mentioned above that the mosquito’s note increased in pitch as
the wings were shortened until a very short stump was left. As long
as these stumps were left a note was heard, and these stumps would
undoubtedly include the apparatus just described, for it is next
and nighest the insertion of the wing into the body. But Dr. Nuttall
found that when this short stump was removed all perceptible sound
ceased, which is certainly an argument in favour of these rods and bars
playing some part in the production of the buzzing, and in opposition
to the view of Howard and others that the buzzing is caused by certain
chitinous structures in the tracheae.
M. J. Perez[7] has carefully gone into the question of the production
of sound in the Diptera. He claims to have shown experimentally that
the stigmata take no part in the production of sound. ‘Les causes du
bourdonnement résident certainement dans les ailes.’ He, too, points
out that if the wings are cut short the notes become more acute, until
the _timbre_ resembles that of certain interrupters which break and
make an electric conductor. This sound we should attribute to the
stridulator described above. M. Perez definitely states that both in
the Diptera and in the Hymenoptera the buzzing is due to two causes:
‘L’une, les vibrations dont l’articulation de l’aile est le siége et
qui constituent le vrai bourdonnement; l’autre, le frottement des
ailes contre l’air, effet qui modifie plus ou moins le premier.’ The
apparatus we have described is, we believe, the mechanism by means of
which the first vibrations are produced.
[7] _Compt. Rend. Acad. Paris_ (1878), lxxxvii, p. 378.
In the same periodical M. Jousset de Bellesme[8] confirms the statement
that both Dipterous and Hymenopterous insects emit two sounds—one deep
and one acute, and states that the latter is usually the octave of the
former. It is this double note which gives rise to the peculiar buzzing
associated with these two orders of insects. M. de Bellesme, like M.
Perez, discards the view that acute sounds are due to any action of the
issuing air in the stigmata, and attributes it to the vibrations of
the pieces of the thorax which support the wing, and which are moved
by the muscles of flight. It is usually stated that these muscles
are not inserted into the wing, but into the sides of the thorax, to
which the wing is so attached that when the lateral walls of this
part of the body are deformed by the action of the muscles the wings
move up and down. But whether this be the case or not, it is clear
that the vibrations of the sides of the thorax caused by the muscles
of flight—and causing the vibrations of the wing—will synchronise in
number with these wing vibrations, and will give forth the same note.
The existence of the higher note —‘usually the octave’ of the one
produced by the wing vibrations—is unexplained by this view. It is,
however, easily explicable if such a stridulating organ as we have
described at the base of the wing in _Anopheles maculipennis_ be found
in other Diptera and in Hymenopterous insects.
[8] _Compt. Rend. Acad. Paris_ (1878), lxxxvii, p. 535.
In our paper Mr. Wilson and I thought it well to figure the upper
surface of the halter as seen under a high magnification. The drawing
showed the hinge on which the halter quivers—and certain basal
papillae, as Weinland[9] calls them. There is little doubt that the
main function of the halteres is that of balancing and orientating the
insect. They may, however, have a secondary function; in some flies
they are known to vibrate with extreme rapidity. It is just possible
that in these rapid vibrations the papillae of the concave surface
rubbing against those of the convex basal plate may produce a note.
As long ago as 1764 von Gleichen-Russworm[10] observed that when the
halteres of the common house-fly are removed the volume of the buzzing
diminished. This, however, in all probability is due to the diminished
activity of the wings. On the other hand, Professor J. Stanley Gardiner
informs us that he has noticed that mosquitos still continue to give
forth a faint note even when their wings are quite at rest, and this
note may possibly be caused by the halteres.
[9] _Zeit. f. wissensch. Zool._ (1891), li, p. 55.
[10] _Geschichte der gemeinen Stubenfliege._ Nuremberg, 1764.
The part which sound plays in the life of the mosquito has not been
very fully recognised. Grassi says that people who are talking are
more liable to be bitten by _Anopheles_ than people who are silent—and
quite properly, we think; people are apt to talk too much, especially
in trains. Joly observes in Madagascar that mosquitos are attracted by
music. When he played a stringed instrument the quiescent mosquitos in
his room began to fly about, and if the windows were open mosquitos
were attracted from the outside into his room, and he notes that
mosquitos are attracted by musicians when at work, or should we say—at
play?
Two curious instances—one recorded by Howard and the other printed
in a letter to _The Times_—of the attraction that electric buzzings
have on these insects may be given. Mr. A. de P. Weaver, an electrical
engineer, of Jackson, Miss., U.S.A., records that, when engaged in
some experiments in harmonic telegraphy, he observed that when the
note was raised to a certain number of vibrations per second, all the
mosquitos—not only in the room, but from the outside—would congregate
near the apparatus, and were, in fact, precipitated from the air
with a quite extraordinary force, hurling their frail bodies against
the buzzing machinery. This machinery formed, in conjunction with
sticky fly-paper, an excellent means of capturing them. Mr. Weaver
then devised a means of electrocuting the pests. He used a section
of unpainted wire screen mounted on a board with pins driven through
the meshes, the heads of the pins being flush with the surface of
the screen. The bodies of the pins were then electrically connected
together, the whole forming one electrode of the secondary coil of an
induction coil, whilst the wire screen formed the other electrode. An
alternating current of high potential was passed, and when the note
was sounded the insects precipitated themselves to their doom, being
electrocuted the moment they touched the apparatus.
A somewhat similar story is told by Sir Hiram Maxim in _The Times_ of
October 29, 1901. One of the lamps in an installation which was put
up in Saratoga Springs, New York, hummed in an agreeable manner, and
he noticed that night after night this lamp was covered with small
insects. On closer examination he found that they were all mosquitos,
and all males.
CHAPTER VII
THE MOSQUITO (_Anopheles maculipennis_)
PART IV
Gnats are unnoted wheresoe’er they fly,
But eagles gazed upon with every eye.
(SHAKESPEARE, _Rape of Lucrece_.)
The eggs of the mosquito are deposited in fresh water, and at first
they are white, but they very rapidly darken until they assume a
polished black appearance. Each egg is 0·72 mm. in length, and its
greatest breadth, which is somewhere about its middle, is 0·16 mm. The
egg is boat-shaped, and one end, as is usual in boats, is slightly
deeper and fuller than the other. The under surface is fluted, and
is marked by a minute network. The upper surface has a coarser
reticulation which divides the surface into nearly equal hexagonal
areas. The rim of the ‘boat’ is thickened, and these thickenings are
regularly ribbed; they extend over above the median third of the egg,
and recall the rounded float which runs along the edge of a life-boat:
and indeed they serve the same purpose, for they are composed of
air-cells, and their function is to keep the boat-shaped eggs right
side upward. Soon after the egg has been laid it is of a greyish-black
colour, but after a certain amount of attrition an outer membrane
splits off—the membrane which has given the egg its reticulated
appearance. This membrane scales off in fragments, and is of a grey
colour. The egg beneath it is glistening black—as shiny and as black as
patent leather.
One curious fact that Professor Nuttall and I noticed in the
life-history of the egg is that when it is drawn by capillary forces
a little way out of the water on to the leaf of a water-plant or some
other half-submerged object, the blunt end always points downwards. Now
the blunt end is the head end, and thus, should hatching take place
whilst the egg is suspended half in the water and half in the air, the
larva will emerge into its proper element and not into the atmosphere.
[Illustration: FIG. 19.—Larva and eggs of _Anopheles maculipennis_.
A, Egg seen from the side, × about 20; _fl_, the float. B, Egg seen
from the upper surface, × about 20; _fl_, ridge of air-chambers, which
acts as a float. C, Very young larval stage, × about 20; _st_, stigma.
D, Fully grown larva, × about 20; _b_, brush _ant_, antenna; _mp_,
palp of maxilla; _st_, stigma; _t_, tergum; _ap_, anal papillae. E,
Flabellum or flap, which overhangs the base of certain thoracic hairs.
F, A palmate hair, highly magnified. (From Nuttall and Shipley.)]
Like other objects floating on the surface, the mosquito-egg slightly
indents the surface. The number of eggs seems to vary. According to
Grassi, each female deposits about one hundred eggs, whilst Howard puts
the number as varying from forty to one hundred. We, however, found in
captivity the female laid about one hundred and fifty. According to
Grassi, the eggs of _A. maculipennis_ lie side by side like the bridges
of boats which span the Rhine, whilst those of _A. bifurcatus_ arrange
themselves with their ends in contact, forming starlike patterns.
Unlike the eggs of the gnat (_Culex_) the eggs of _Anopheles_ do not
adhere together, and the result is they are very readily scattered
by the wind. But in sheltered places, like a laboratory aquarium, if
undisturbed, the Italian Professor found that they tended to congregate
together, as indeed do most minute objects floating on the surface of
the water. Our observations did not entirely confirm those of Grassi.
In Cambridge, at any rate, we found the eggs in our aquaria always
scattered. Very frequently empty egg-shells were met with, but they too
were scattered. As a rule, in nature, the ova are deposited in water
rich with algae or other vegetable life, and they are more frequently
in shallow than in deep water, the temperature of shallow water being
naturally somewhat higher.
On the second or third day after oviposition (and this depends upon the
temperature), the young larva leaves the egg and begins to swim in the
water. The egg hatches by the detachment of a cap-like portion of the
anterior end of the egg-shell. There is no visible ring indicating the
limits of this operculum, but the cap is usually more or less of the
same size. Opinions differ as to how far desiccation interferes with
development of the larva in the egg-shell. They do not seem to be able
to stand more than forty-eight hours of drought. There is no evidence
that they can survive throughout the winter period. Everything that we
know indicates that the egg must pass this period within the mother’s
body, and that they only attain maturity in early spring, when the
weather becomes warmer.
The larva of the mosquito is one of the most fascinating objects one
can watch under the microscope. It is very complex, and consists of the
usual arthropod regions of (1) the head, (2) the thorax, and (3) the
abdomen.
[Illustration: FIG. 20.—Side view of head of a fully grown larva of
_Anopheles maculipennis_. _b_, Brush; _c_, antenna; _d_, palp of
maxilla; _m_, hooked hairs at edge of maxilla; _p_, median tuft of
hairs; _r_, thickened rim of chitinous covering to head; _s_, large,
feathered hairs which overhang head; _t_, mandible; _u_, larval eye;
_v_, eye of adult, forming above and behind _u_. (From Nuttall and
Shipley.)]
Without going into the question of how many typical somites make up the
head, we must state that the thorax has the typical number of three,
much fused together, and the abdomen nine. The first seven of these
are very much alike; the eighth, however, bears the large stigmata or
orifices of the breathing system, and the ninth a number of beautifully
arranged hairs, by means of which the larva to a great extent steers
itself. The head resembles two-thirds of a sphere, and is covered with
a complete and clearly defined brown, chitinous case. The eyes are
lateral, and on each side we have both a simple and a compound eye. In
front of each eye is a little protuberance, which carries the antenna,
and between these two eminences a band of pigment runs across the
head, from which six symmetrically placed immovable feathered hairs
project, wreathing the head, as it were, with a halo. There are many
other hairs on the head, whose number and shape are of great systematic
importance. The anterior edge of the head carries on each side of its
under surface a conspicuous brush, very like a shaving-brush, the
constituent hairs of which are arranged in a spiral, and it is these
brushes which sweep the food into the mouth of the young and voracious
larva. The base of this brush is so arranged that when depressed and
bent towards the mouth the two brushes approximate, but each brush can
move independently and often does so: one may be depressed towards the
mouth, whilst the other remains erect.
[Illustration: FIG. 21.—Ventral view of head of a fully grown larva
of _Anopheles maculipennis_. _b_, Brush; _c_, antenna; _d_, palp of
maxilla; _j_, stout hairs of mandible, which arrange the brush; _k_,
teeth of mandible; _m_, hooked hairs at edge of maxilla; _p_, median
tuft of hairs; _q_, the ‘underlip’ of Meinert, or metastoma; _r_,
thickened rim which passes into the soft tissues of the neck. (From
Nuttall and Shipley.)]
The larva passes its life hanging on to the under surface of the
surface-film of the water, its dorsal surface being uppermost. In fact,
as Sidney Smith pointed out about the sloth, ‘it passes its life in a
state of suspense, like a young curate distantly related to a bishop.’
But, since these larvae feed on any kind of organic débris that
floats up to the top and is there arrested by the surface-film, it is
obviously important that the brushes which sweep together these organic
particles and carry them to the mouth should be next the surface, and
to effect this the head must rotate through an angle of 180°; and
the head does in fact turn upside-down on the neck so sharply and
accurately that, as it comes into position, you almost think, as you
are watching it, that you hear a click, just as you do when you rotate
the diaphragm of a microscope.
The mouth parts now begin to vibrate upwards and forwards, and the
brushes are bent downwards, backwards, and inwards. Round the mouth is
a small space, the walls of which are completed by the mandibles, and
into this space the brushes are suddenly bent back, at the same time
the mandibles and maxillae move forward to meet them. This movement may
take place as many as 180 times a minute, and it produces a current
converging in concentric curves towards the above-mentioned chamber.
The water filters out between the sides, and any particle of food is
retained by the hairs or by the mouth appendages; from time to time
the mandibles are brought together, and their stiff bristles are run
through the brushes as one’s fingers run through a beard;[11] at other
times the brushes disappear far into the mouth, and then are slowly
withdrawn, passing through the comb-like bristles on the mandibles. The
brushes are frequently swallowed, and are withdrawn in little jerks,
so that the maxillae have every opportunity of combing any nutritive
particles out of them. The whole operation is a most fascinating one to
watch.
As far as one can judge, the currents set in motion by the action
of all these forces extend in an area equal to twice the length of
the larva, or even more. The currents are in the plane just below
the surface-film, and any organic matter lighter than water is swept
towards the mouth. In fact the larva sweeps the lower side of the
surface-film of the pond or puddle just as a careful housemaid might
sweep spiders and flies off a ceiling with a hand-brush.
The principal food-supply of the larva consists of the spores of
fresh-water algae, diatoms, particles of _Spirogyra_, and any other
organisms which do not penetrate the surface-film. Occasionally the
larvae devour the decaying leaves of duck-weed (_Lemna_), and sometimes
they attack their dead fellows.
[11] If you have a beard.
Grassi found the intestine of the larva to contain protozoa,
unicellular algae, and other organic detritus. In course of time some
object too big for the larva to swallow is brought to its mouth by the
currents, but after a very short struggle this is rejected. The minuter
particles accumulate in the chamber for a certain time, and then are
swallowed by a gulp-like motion and thus pass into the oesophagus.
[Illustration: FIG. 22.—A comparison between the various stages in the
life-history of the mosquito (_Anopheles_), on the left, and the gnat
(_Culex_), on the right.
ANOPHELES CULEX
_IMAGO_
_PUPA_
_LARVA_
_OVA_]
CHAPTER VIII
THE MOSQUITO (_Anopheles maculipennis_)
PART V
Amongst aquatic larvae, the most beautiful and delicate are those of
numerous species of gnat.—(GORING AND PRITCHARD’S _Micrographia_,
1837.)
In the young larva of _Anopheles_ the head is broader and deeper than
the thorax, but in the older larvae the segments that succeed the
head have at least twice its diameter. It is a characteristic of true
flies, or Diptera, that the thorax should not exhibit that separation
into three divisions which is so usual in the less specialised
insects—such as the cockroach and this is peculiarly true of the larva
of the mosquito—at any rate, so far as its external structure goes.
The abdomen of the larva consists of nine free segments; the third,
fourth, fifth, sixth, and seventh of these bear palmate hairs on the
dorsal or upper surface, something like hands with fourteen ‘fingers’
spread out. These hairs adhere to the under layer of the surface-film
of the water, and help to maintain the animal in a horizontal position
just below that film. When the larva relaxes its hold and sinks into
the water, it not infrequently carries with it air-bubbles enclosed by
these fourteen ‘fingers.’
The eighth abdominal segment bears the stigmata or the openings
of the respiratory apparatus, and the ninth segment has abandoned
the flattened and square cross-section of its predecessors, and is
cylindrical and tapering. The posterior end of the body is cut off
sharply. Round the posterior opening of the alimentary canal are
four white, soft papillae, which are well supplied with tracheae and
are capable of contracting and expanding. Above these are four very
prominent hairs, two median and two lateral, and ventrally to the ninth
abdominal segment is a fan-shaped arrangement of hairs springing from
two pieces of very complicated structures. These hairs seem to act to
some extent as a rudder, and they probably serve as an accessory organ
of locomotion. Possibly they have also a sensory or tactile function,
and act, as so many posterior filaments do in insects, as antennae
‘from behind.’
We have referred above to the respiratory openings, and, indeed, these
are the key to the whole situation. Close these openings— as they
can be closed by floating petrol or other oil on the surface of the
water—and ‘the trick is done.’ The larvae and the pupae can no longer
breathe, and there is thus no imago to “carry on.” In _Culex_ (the
gnat), these respiratory orifices are borne on a long tube directing
dorsalwards—a tube which is larger and longer than a segment of the
body, and whose presence gives the larva the appearance of a Y with
slightly unequal limbs. These breathing-openings are of the greatest
complexity, but the outstanding fact is that these stigmata pierce
through the watery film and put the respiratory system of the larva
into communication with the atmosphere of the whole cosmos. If anything
frightens the larva, certain side-pieces and flaps fold suddenly
backwards and over the stigmata, the connexion through the surface-film
is broken, and the little larva, like a German submarine when it
sights an English battleship, darts below, frequently carrying with it
the drop of air attached to the rim of the respiratory recess which
surrounds the openings of the two stigmata.
Not infrequently the larva ceases to lie parallel to the surface of the
water, its palmate hairs are put out of action, and then its body hangs
down into the water, but it still maintains its respiratory connexion
with the outer air through these breathing-pores. From time to time
the hairs mentioned above are brushed over by the mouth parts and
cleaned of any débris.
The larvae, when they leave the surface-film sink by their own
weight; but they not infrequently swim actively downwards, their
swimming action being very like that of an eel. When returning
to the surface they are entirely dependent upon their powers of
swimming, being slightly heavier than water. When the tail reaches the
surface-film the larvae are at once arrested, and immediately cease
their swimming-movements. They invariably move tail forwards, and
the hairs which we have mentioned above at the posterior end of the
body undoubtedly act as ‘buffers’ or ‘fenders.’ As a rule, when they
are above, they are actively engaged in feeding; but at the bottom
they lay inert, as though feigning to be dead. Kept in a glass beaker
they are apt to lie with their respiratory apparatus attached to the
concave film, which capillary attraction draws up on the surface of the
glass. Their heads then point towards the surface of the beaker. If
forcibly kept below—say, by submerging them under a watch-glass—they
are frequently enabled to breathe by attaching the openings of their
respiratory apparatus to an air-bubble.
The general colour of the larva is a mottled brown, darkening where the
chitin thickens. The older larvae are to some extent green, possibly
due to their food; but this green colour is not by any means confined
to the alimentary tract. After moulting, the issuing larva is a uniform
light lavender colour, which, however, very soon darkens.
A strong wind passing over a pool where _Anopheles_ eggs, larvae, or
pupae are floating, will gradually pile them all up on the side towards
which it is blowing. The _Anopheles_ larvae undoubtedly are braver than
those of the _Culex_—that is to say, a disturbance which will send all
the _Culex_ larvae scurrying to the bottom will leave the _Anopheles_
larvae unmoved.
When first hatched the larvae measure somewhere about 0·7 mm. to 0·95
mm., but when ready to pupate they have attained the length of 7 mm.
The rate of development is greatly influenced by the temperature, and
a few cold days will markedly retard the larval growth. In warm sunny
weather, larvae will pupate between the second and third week, but
larvae taken in August (if the autumn be cold) do not attain their full
growth until November. The young larvae undoubtedly die in considerable
numbers, and the act of pupating is also attended with certain and
varying dangers. Out of 834 larvae and pupae caught in Cambridgeshire,
636 were small larvae, measuring less than 4 mm.; 181 were large
larvae, measuring up to 7 mm. But only 17 pupae were taken. There are
other facts which show that the larvae under natural conditions succumb
in very considerable numbers.
[Illustration: FIG. 23.—Side view of late pupal stage of _Anopheles
maculipennis_. _f_, The stigma opening at end of trumpet-like
projections. (From Nuttall and Shipley.)]
When the larva is about to turn into a pupa it comes to rest, and now
the thoracic regions are more swollen than ever. Soon a dorsal slit
appears along the larval cuticle and the pupa slowly, but gradually,
emerges through this slit and leaves the larval chitinous cuticle
behind it. On first emerging, the pupa measures about 6·5 mm., the head
and thorax making up one-third of this. During the last larval stage
many of the pupal organs have been re-forming and are more or less
visible through the cuticle. The mouth parts and limbs of the third
stage—the future imago—show no relation to those of the larva. They
are there enclosed in their respective sheaths, but these are quite
independent of the larval ‘appendages.’ The respiratory trumpets,
which, as in the larva, pierce the surface-film, are ready to act as
breathing-organs. Whereas the larvae breathe through two stigmata
at the posterior end of the abdomen, the pupae breathe through two
respiratory trumpets issuing from the anterior dorsal surface, and it
is these trumpets, together with certain palmate hairs, which support
the pupae in the right position and put the respiratory organs at this
stage into communication with the outer atmosphere. During the pupa
stage _Anopheles_, like the pupa of other insects, takes no food.
The pupa is something like a tadpole, with its tail bent under its
body and flapping up and down, instead of from side to side. The whole
pupa is enclosed in a thin semitransparent membrane, through which the
organs of the adult can readily be seen. As it grows older its colour
darkens. Until about the time when it will give rise to the fly, the
pupa floats quietly at the surface, breathing through its respiratory
trumpets. When disturbed it shows considerable activity, and it is by
no means always easy to capture by means of a pipette. At the least
sign of danger it darts below with a series of intermittent strokes
and rests at the bottom of the water. Its own buoyancy brings it back
to the surface, as, unlike the larva, it is lighter than water. Not
only has it a certain amount of air in its tracheae, but there is a
reservoir of air at the posterior end of the thorax which acts as a
very efficient float. When retreating below the surface the respiratory
trumpets usually carry down with them two minute air-bubbles.
[Illustration: FIG. 24.—A, Side view, B, ventral view, of the pupa of
a male _Anopheles maculipennis_; C and D, the same views of the female
pupa.]
The sex of the pupa can be determined by the lobes at the posterior
end of the tail: A and B (Fig. 24) representing the male, and C and D
the corresponding parts of the female. The duration of the pupal life
is generally three to four days, but conditions of temperature and the
state of the natural surroundings exert considerable influence upon
the rate of development. Howard has pointed out that the addition of
creosote or creosote-oil to the water in which the larvae are living
hastens the metamorphosis into pupae, and the pupa stage is passed
through in as short a time as fifteen hours instead of the normal
forty-eight hours of the warm waters of the Southern States in America.
It has also been observed that showery weather hastens the rate of
development.
When the adult mosquito is about to emerge, a certain amount of
air is secreted under the chitinous casing of the pupa. A fine
streak containing air appears along the back, extending between the
respiratory trumpets and the base of the head. This central streak
gradually passes backwards until it reaches the seventh abdominal
segment, and then suddenly the pupa extends its abdomen so that it
floats parallel to the surface of the water instead of being under the
rest of the pupa’s body. The chitinous integument now splits along the
median dorsal line, and through the slit thus made the thorax of the
adult mosquito now protrudes. By gradually pressing its abdomen against
the pupa-case, the body of the perfect insect is slowly but gradually
raised above the surface of the water. The head is pulled backwards
and upwards, and millimetre by millimetre the mouth parts, the palps,
and antennae are withdrawn, and at first remain bent backwards beneath
the body of the insect. Gradually the bases of the wings and the
abdomen emerge, and soon the wings are freed and immediately flatten
out and begin to harden. The legs and the tip of the abdomen alone now
remain to be dealt with. At this stage the insect projects far beyond
the anterior end of the pupa encasement, and somewhat resembles an
exaggerated figurehead on a ship. The pupa-case is still filled with
air, and acts as a float to support the emerging insect. At last the
front legs are being freed, the second and third pair of legs soon
follow, and now the insect is standing on the surface of the water
raised on its tarsal joints, the tip of the abdomen being the last part
to free itself from the pupa-case.
[Illustration: FIG. 25.—Imago of a mosquito extracting itself from the
pupa-case, which floats on the surface of the water. Magnified. (From
Guiart.)]
The exit of the fly is naturally a very critical period in its
life-history, and in many cases it is fatal. The freeing process takes
between five and ten minutes. When undisturbed the emergent fly rests
for a time until its wings and limbs are sufficiently hardened to
enable it to fly, or at least to walk about. Sometimes the mosquito
takes its first flight straight from the pupa-case; at other times
it rests awhile before taking to the air. The young imago is pale in
colour, the thorax being brown and the abdomen transparent, with a
greenish tinge. At first the abdomen is much longer than it is later,
for, almost immediately after the mosquito’s exit from the pupa-case
its abdomen begins to contract, and from its hinder end four or five
drops of a glistening, greenish-white fluid are exuded.
The newly born imagines generally take to flight between five and ten
minutes after they have emerged, and they at once begin to darken in
colour, and in two hours assume the normal dusky colour of the adult.
If anything hinders the insect from properly extending its limbs
immediately on issuing from the pupa-case, the parts harden and remain
distorted throughout life.
* * * * *
Anyone who has spent a day or two in Lille or Bruges, or other towns
in Picardy and in Southern Belgium, will understand why, as my Uncle
Toby has it, ‘Our army swore terribly in Flanders.’ The incessant and
tireless biting of mosquitos would make any army swear, even though
they were ignorant—as my Uncle Toby’s army certainly was ignorant—that
the gnats, as they called them, conveyed tertian and quartan ague. In
Europe the trouble is a summer or early autumn trouble; but our troops
are fighting in many tropical and sub-tropical countries, where the
mosquitos—like the poor—are always with them.
That the plague can now be checked is shown by the making of the Panama
Canal; and that this check is due to British science is shown by the
work on the life-history of the malarial organism, first investigated
by Sir Ronald Ross, and later, as regards the human parasites, by
certain Italian savants. It is also due to the public health services
of one or two British medical officers of health in the East. _Their_
methods have been applied and improved by those responsible for the
elusive channel which now at times separates North from South America.
We have seen that the larva and the pupa hang on to the surface-film
of the water by means of certain suspensory hairs, and by the
openings of their breathing-apparatus. Anything which prevents the
breathing-tubes reaching the air ensures the death of the larva and
pupa, and then there is no issuing adult—hence the use of paraffin on
the pools or breeding-places. It, or any other oily fluid, spreads as
a thin layer over the surface of the pools and puddles and clogs the
respiratory-pores and the larvae or pupae die of suffocation.
In Ismailia the disease has been reduced to an amazing extent, and
remarkable results have followed the use of these preventive measures
at Port Swettenham in the Federated Malay States. Within two months
of the opening of the port in 1902, 41 out of 49 of the Government
quarters were infected, and 118 out of 196 Government servants were
ill. Now, after filling up all pools and cleaning the jungle, no single
officer has suffered from malaria since July 1904, and the number of
cases amongst the children fell from 34·8 to 0·77 per cent. The only
melancholy feature about this wonderful alleviation of suffering, due
to the untiring efforts of the district surgeon, Dr. Malcolm Watson, is
that his fees for attending malarial cases dropped to zero.
Thus, even ten years ago, a considerable degree of success had attended
the efforts of the sanitary authorities—largely at the instigation of
Sir Ronald Ross—all over the world, to diminish the mosquito-plague.
It is, of course, equally important to try to destroy the parasite
in man by means of quinine. This is, however, a matter of great
difficulty. In Africa and in the East nearly all native children
are infected with malaria, though they suffer little, and gradually
acquire a high degree of immunity. Still, they are always a source of
infection; and soldiers stationed in malarious districts should always
place their dwellings to the windward of the native settlements.
Knowing the cause, we can now guard against malaria; mosquito-nets and
wire-protected windows and doors are a sufficient check on the access
of _Anopheles_ to man. If the mosquito and man could only be kept
permanently apart, we might hope for the disappearance of the parasite
from our fauna. In relieving man from this world-wide pest, all genuine
lovers of animals will rejoice that we are also relieving the far more
serious lesions of one of the most delicate and beautiful insects that
we know.
It has always been a source of surprise to me that the great resources
and the very evident enthusiasm of the anti-vivisection societies have
not been turned in this direction. In the malarial parasite, we have a
most potent vivisector of the entrails of one of the most charming and
graceful of creatures, whose poetry of movement is hardly approached
and never equalled by the ladies of the front row of the ballet. A
little help, a very little help, would free these fascinating flies
from a form of trouble far worse than that the human alternative host
suffers. Yet, as far as I know, these societies and the societies for
the prevention of cruelty to animals have declined to help in any
way, and have knowingly allowed thousands of millions of animals to
perish annually by a most painful death, and have never stretched out a
helping hand to the fairy-like and fascinating mosquito.