COCKROACHES; EARWIGS; THE GREAT GREEN GRASSHOPPER; THE
WATER SCORPION; THE WATER BOATMAN;
CORIXA.
The next insect to come within range of our pocket lens is the Common
Cockroach (_Blatta orienta´lis_[15]), popularly misnamed the
Black Beetle. We shall have no difficulty in procuring material for
examination. Housekeepers will tell us that these creatures are only
too plentiful.
In the last chapter we dealt with Sheath-winged Insects--the
Coleop´tera. Cockroaches belong to the Orthop´tera, or Insects with
Straight Wings. The mouth-parts resemble those of Beetles. The chief
differences that mark off the Cockroaches and their kin from the
Beetles are the incomplete metamorphosis which the former undergo, and
the character of the wings. Straight-winged Insects, when they leave
the egg, differ little in shape from the adult, except in the fact that
they have no wings; and these appendages are absent, or so small as
to be useless for flight in many species. When wings are present the
first pair are of little or no use for flight. They are not, however,
hard chitinous sheaths, meeting in the middle line--that is, straight
down the centre of the back--but of a flexible leathery or membranous
substance, and they usually overlap each other at the tips. The hinder
wings are large and nearly semicircular. The principal veins radiate
from the centre to the circumference, like the sticks of a fan, and
when the wings are folded up they lie straight along the upper surface
of the abdomen. It is from this fact that the Order derives its name.
There are two great groups, or sections, of Straight-winged
Insects--those that run, like the Cockroaches, and those that leap,
like the Grasshoppers. No Straight-winged Insect is aquatic.
The Common Cockroach, now so abundant, is not a native, but an
importation from Asia; though how it reached this country is not quite
certain, probably by way of Holland. It seems to have established
itself in London by the end of the sixteenth century, and some two
hundred years later we find Gilbert White recording (in or before 1790)
that ‘a neighbour complained that her house was overrun with a kind of
black beetle, or, as she expressed herself, with a kind of black-bob,
when they got up in the morning before daybreak. Soon after this
account I observed an unusual insect in one of my dark chimney closets,
and find since, that in the night they swarm also in my kitchen....
The male is winged, the female is not, but shows something like the
rudiments of wings, as if in the pupa state.... They are altogether
night insects, _lucifugae_, never coming forth till the rooms are
dark and still, and escaping away nimbly at the approach of a candle.’
This description leaves no doubt as to what the ‘black-bobs’ really
were. This name seems to have dropped out of use, and it would be well
if ‘black beetle,’ in the sense of Cockroach, were also allowed to
drop, for the term contains just as many errors as words.
We may make our first acquaintance with these insects by keeping some
specimens in confinement. A tin box, with a glass lid, will make a
capital dwelling for them. Some paper should be put in, for them
to hide in away from the light, and there can be no difficulty in
providing them with food. ‘Bark, leaves, the pith of living cycads,
paper, woollen clothes, sugar, cheese, bread, blacking, oil, lemons,
ink, flesh, fish, leather, the dead bodies of other cockroaches,
their own cast skins and empty egg-capsules, all are greedily
consumed. Cucumbers, too, they will eat, though it disagrees with them
horribly[16].’
We have Dr. Sharp’s authority for the statement that in confinement
these insects are rather amusing pets, as they ‘occasionally assume
most comical attitudes, especially when cleaning their limbs. This they
do somewhat after the fashion of cats, extending the head as far as
they can in the desired direction, and then passing a leg or an antenna
through the mouth; or they comb other parts of the body with the spines
on the legs, sometimes twisting and distorting themselves considerably
in order to reach some not very accessible part of the body[17].’
The prejudice against these insects is, however, so strong, that most
people will prefer to examine dead rather than living specimens, on
account of the disagreeable odour of the latter. This odour is due to
a fetid excretion from the mouth, and if the specimens are killed by
dropping them into boiling water, this will be discharged, and after a
little while they may be taken out with a pair of forceps, and put into
spirit for preservation. If they are dropped alive into spirit, the
excretion will communicate its strong scent to the preserving medium,
and this should be changed before the insects are examined.
From Fig. 32 we may get a general idea of the appearance presented by
a male or female, lying back upwards in a small glass dish, ready for
examination with the pocket lens. The female may be distinguished at a
glance by her wingless condition--only rudiments of wing-cases being
present, and no wings--and her broader abdomen. In life she does not
stand so high upon her legs as does the male, and her abdomen trails
along the ground. The male does not acquire his wings till the last
moult.
[Illustration:
_Female._ _Male._
FIG. 32.--Cockroaches.]
As the Cockroach lies back uppermost in a glass dish, the head is
almost concealed. This is especially the case, unless the insect is
flattened out in some way, or pinned down to a piece of weighted cork.
There will thus be, apparently, two, instead of three main divisions.
This arises partly from the fact that the head is deflexed, or bent
down so that the mouth is turned towards the rear, and partly because
the first segment of the thorax bears a chitinous shield, roughly
semicircular, which covers so much of the head as would otherwise be
visible.
The difficulty, however, may be easily got over, by reversing the
position of the insect, and raising the head with a needle. The
antennae will attract attention by their great length. In the male
insect they exceed, while in the female they fall a little short of,
the total length of the body. They are well worth examination. Even a
low power will show that they consist of a number of joints--usually
from seventy-five to ninety. The three basal joints are much larger
than the rest, and in the female the third basal is nearly as long as
the first. All these joints are thickly set with stiff hairs directed
forwards. At the outer side of each antenna is a compound eye, and on
the inner side is a pale spot, the _fenestra_, which in the males
of some foreign Cockroaches is replaced by a simple eye.
If Cockroaches are kept in confinement, and forced out into the light,
the constant motion of the antennae will satisfy the observer that they
are of great use to their owners. By means of these organs they not
only discover their food, but become by some means, probably by the
motion of air-waves, aware of danger that threatens them. Belt, in his
_Naturalist in Nicaragua_ (p. 110), speaking of the Cockroaches
that infest houses in the tropics, says, ‘They are very wary, as they
have numerous enemies--birds, rats, scorpions, and spiders; their long,
trembling antennae are ever stretched out, vibrating as if feeling the
very texture of the air around them; and their long legs quickly take
them out of danger.’ It is not given to every one to visit the tropics,
but we may all use our eyes in observing the common insects that abound
in our country, and in doing this we shall strengthen the habit of
observation, and very often find confirmation of what we read of the
habits of insects in distant lands.
Sir John Lubbock[18], in treating of the sense of smell in Insects,
says that ‘Plateau put some food of which cockroaches are fond on a
table, and surrounded it with a low circular wall of cardboard. He then
put some cockroaches on the table: they evidently scented the food,
and made straight for it. He then removed their antennae, after which,
as long as they could not see the food, they failed to find it, even
though they wandered about quite close to it.’
The large kidney-shaped compound eyes are sure to attract attention.
It is worth while to take out and break up an eye, gently washing out
the pigment. If we do this, and then examine it with the pocket lens,
we shall have some idea of the multiplicity of lenses in the eye of a
Cockroach, each of the six-sided facets being a lens.
Next come the mouth parts, which may be run over very quickly, for
those of Beetles are formed upon the same plan, and from this primitive
plan are derived the mouth parts of all other Insects, of whatever
character they may be. To examine the mouth organs the insect must be
turned on its back, and the _labrum_ (_a_), or upper lip,
raised with a needle, so as to allow of a general view of the rest.
Then the jaws or mandibles (_b_) may be picked out with a needle.
These jaws are strongly toothed, and work from side to side, and it
is easy to see that they are very efficient organs. The lower jaws
(_c_), or _maxillae_, lie below, and are compound organs,
each being made up of several parts--the base, called the _cardo_
or hinge (not shown in the illustration, but connected at right angles
by a joint with the lower part, the _stipes_). From the stipes
rise the _galea_, or helmet, on the outer side; and, on the
inner side, the _lacinia_, to which the name maxilla is often
applied, though it properly belongs to the whole. At the base of the
_galea_ is inserted the five-jointed maxillary palp, thickly set
with hairs, and probably an organ of touch.
[Illustration: FIG. 33.--Mouth parts of a Cockroach.]
By examining the maxillae (_c_) before they are separated, and
comparing them with the _labium_ (_c_) or under lip, which closes the
mouth from below, it will be evident that there is no slight similarity
between them. Nor is this strange: for the under lip consists of the
second maxillae joined at their bases, which form the _submentum_ (_s_)
and _mentum_ (_m_). (The former is the small, the latter the large
white basal portion; the vertical line in the illustration shows the
mental suture, and should be traced in the dead insect.) The organs in
the centre constitute the _ligula_; and on each side of the labium is a
three-jointed palp (_labial_), like that on the maxillae, thickly set
with hairs, and with a similar function. It is well to work over the
mouth parts a few times till the relation between the maxillae and the
labium is seen and understood. The internal tongue (_d_) is attached to
the inner side of the labium.
Now, still working on the under side of the insect, the three segments
of the thorax are to be made out, and one cannot fail to notice the
great size of the first joint (the _coxa_) in all the legs, and
that these joints seem to serve as shields to protect the under side
of the thorax. Then the different parts of the legs should be traced,
and compared with Fig. 23 on p. 44. The spiny armature of the tibiae is
to be noticed, as are the claws, between which is a projecting lobe,
though this is absent in immature specimens. We shall find that the
appendages of the thorax are the same as in the Margined Water Beetle.
It is well to take as little as possible on trust, and to verify
everything that we possibly can.
Now we may reverse the position of our subject, and having cut off
the wing-cases, which are technically called _teg´mina_, examine
the wings. These may be gently unfolded with a needle or a camel’s
hair brush, when the longitudinal method of folding will be clearly
seen, and the difference of the veining from that of the wings of
the Margined Water Beetle will be apparent. A female should also be
examined, and the small tegmina cut off, so as to see that not even the
rudiments of wings are present.
The Cockroach breathes like other adult Insects, and the spiracles
are ten in number--two on the thorax and eight on the abdomen. The
thoracic spiracles may be pretty readily seen, but those on the abdomen
are not so easy to make out. But by cutting away, with a fine pair
of scissors, the edges of the plates that cover the upper and under
surfaces of the abdomen and the membrane that unites them (Fig. 34), we
may discover them as the open ends of small tubes. While dealing with
the insect in this fashion, it will be easy to take out a piece of the
tracheal tube, which may be compared with Fig. 28.
[Illustration: FIG. 34.--Cockroach, showing Spiracles.]
The abdomen consists of a series of rings or segments, the exact number
of which is rather difficult to decide, from the fact that some are
concealed and others altered in form. Dr. Sharp[19] says that ‘it is
considered that ten dorsal and ten ventral plates exist, though the
latter are not so easily demonstrated as the former.’ In the male, ten
above (dorsal) and nine below (ventral), and in the female two less in
each case, may be made out without dissection.
From the sides of the tenth segment two organs, the _cerci_
(Fig. 35, _a_), are given off, one on each side. These may be
distinguished from the styles of the males by their presence in both
sexes. Our inch lens will show that each cercus consists of sixteen
rings. If we use the half-inch, we shall see that each ring is set with
hairs of different lengths.
When we have got so far it may be well to compare the structure of
a _cercus_ with that of an antenna (p. 67). In each we have a
succession of jointed rings giving flexibility to the organ, and the
rings in each case are studded with hairs. It has been shown pretty
conclusively--and we may verify the experiments--that the antennae are
sense-organs. Are we not justified in coming to the conclusion that,
since the antennae and the cerci resemble each other in structure,
they also resemble each other in function? If the Cockroach receives
sensations by means of the antennae, is it not probable that it also
receives sensations by means of the cerci?
Having worked over the Cockroach from the outside, it will be
advantageous to get some acquaintance with its internal anatomy.
This is not a difficult matter. The specimen is to be pinned down,
under water, with its back uppermost. The wings having been removed,
a longitudinal cut is to be made down the centre from the posterior
part of the abdomen to the back of the head, and the two sides of the
integument turned back. Or the junction between the upper and lower
plates on each side may be cut through with a cutting needle, and the
whole integument removed.
The first task is to clear away the fat-body, a whitish substance
which overlies the chief organs of the body. When this is picked to
pieces and floated off the digestive system will be exposed. After
this has been worked over a few times there should be no difficulty in
dealing with similar parts in other Insects. At the back of the head
lies the gullet or oesophagus leading into the crop (_c_), at the
base of which lies the gizzard (_g_). The interior of this organ
is furnished with six strong chitinous teeth, with small ridges of
the same substance between them. Towards the posterior end are six
cushions, all set with fine bristles. Behind this comes the stomach
(_v_), into which open seven or eight tubes, closed at one end,
and between it are the Malpighian tubes, which are concerned in the
process of excretion. The small intestine (_co_) succeeds, and
behind this is the rectum (_r_).
[Illustration: FIG. 35.--Alimentary Canal of Cockroach.]
It will be interesting to separate the gizzard from the crop (_c_)
and stomach (_v_) and break it open with a couple of needles, so
as to examine the teeth, which will be more easily made out if the
opened organ be allowed to soak for a time in a solution of caustic
potash.
Similar teeth-like processes are found in the gizzards of many other
Insects, and their presence has given rise to some strange ideas.
Swammerdam[20] says, ‘I preserve also the threefold stomach of a
locust, which is very like the stomach of animals that chew the cud,
and particularly has that part of the stomach called Echinus[21] very
distinctly visible. I do not, therefore, doubt but locusts chew the
cud, as well as the animals just mentioned. Indeed, I persuade myself
that I have seen this.’
Somewhat similar teeth-like processes exist in the Lobster, the Crab,
and the Crayfish. ‘Professor Plateau has expressed a strong opinion
that neither in the stomach of Crustacea nor in the gizzard of Insects
have the so-called teeth any masticatory character.’ He adopts
Swammerdam’s comparison, but considers them strainers, not dividers of
the food[22].
We may be fortunate enough to meet with some specimens of the American
Cockroach (_Periplane´ta america´na_, Fig. 36), a much larger
species, which has established itself in some few places in this
country. At the Zoological Gardens, Regent’s Park, it is abundant, and
has almost, if not entirely, driven out the common form. Mr. Bartlett
believes that it was introduced in cases in which animals have been
sent over from America. Both sexes are winged. They not only possess
organs of flight, but use them. If one visits the Gardens, there will
be no difficulty in getting specimens; and it is interesting to compare
the points of agreement in and of difference between this animal and
our common form.
[Illustration: FIG. 36.--American Cockroach (male).]
The Earwig (_Forfic´ula auricula´ria_) is common enough to furnish
us with plenty of specimens on which we may employ our pocket lens. Any
garden in the summer months will yield an ample supply. Earwigs, like
Cockroaches, are light-shunning insects, and love to hide themselves in
the corollas of flowers; and it is probably from their habit of seeking
to conceal themselves that they have acquired their bad reputation--by
no means confined to our own country--of creeping into the ears of
persons lying asleep, and causing death by getting into the brain. Such
an occurrence is beyond the bounds of possibility. No insect of this
size could pass the drum of the ear.
We may easily keep these insects and observe their movements, if we
put them into a wide-mouthed glass bottle and supply them with food.
They are extremely fond of the flowers of the dahlia; but a dahlia
would offer too many hiding-places, so we will put into the bottle some
nasturtium flowers, or any others with a bell-shaped corolla.
If we get a colony in spring we may watch the care of the female for
her eggs. According to Kirby and Spence[23], ‘she absolutely sits
upon her eggs, as if to hatch them--a fact which Frisch appears first
to have noticed--and guards them with the greatest care. De Geer
(_Mémoires_, iii. 548) having found an earwig thus occupied,
removed her into a box where was some earth, and scattered the eggs in
all directions. She soon, however, collected them one by one, with her
jaws, into a heap, and assiduously sat upon them as before. The young
ones, which resemble the parents, except in wanting elytra and wings,
... immediately upon being hatched creep like a brood of chickens
under the belly of the mother, who very quietly suffers them to push
between her feet, and will often, as De Geer found, sit over them in
this posture for some hours.’ Mr. Kirby adds: ‘This remarkable fact I
have myself witnessed, having found an earwig under a stone which I
accidentally turned over, sitting upon a cluster of young ones, just as
this celebrated naturalist has described.’
Like the Cockroaches, Earwigs undergo an incomplete metamorphosis.
When the young leave the egg they resemble their parents, as may be
seen from the immature forms represented in Fig. 37. The resemblance
becomes greater at each successive moult.
[Illustration: FIG. 37.--Larva and Pupa of Earwig.]
In working over these insects, the forceps, or pincers, at the end
of the abdomen will attract attention. They are found throughout the
family, but little is known of their function. It is said that they
are used to aid in folding the wings, and tucking them under the
wing-covers. This can scarcely be their only function, for they are
found in species that have no wings. Probably they serve as organs
of defence and, to some slight extent, of offence. When the abdomen
is curled up, these forceps certainly give the insect a threatening
appearance. They cannot, however, do much harm.
These forceps differ in shape in the male (Fig. 38) and female, the
blades being almost close together in the latter. In the males they
differ considerably in size. Of 583 mature males taken in one day in
the Farne Islands, and examined by Messrs. Bateson and Brindley, the
forceps varied in length from 2·5 mm. to 9 mm.[24] These are called
respectively ‘low’ males and ‘high’ males. The latter are in all points
larger than the former, and have been described as a separate species,
‘but it was impossible to get reliable measurements of the total
length, owing to the fact that the abdominal segments telescope into
each other’ (cf. p. 30).
After examining the antennae and dissecting out the mouth organs, the
peculiar overlapping or imbrication of the plates of the abdomen
should be looked for; and on the membrane that connects them the
spiracles may be detected.
The wings and the complex method of folding have led some systematists
to rank the Earwigs as an Order, while some others rank them as a
Sub-order. For the present, at any rate, we need not concern ourselves
about this. It is enough for us to know that they are closely related
to the Orthop´tera.
As we look at the Earwig from above, the wing-cases recall to our mind
those of the Devil’s Coach Horse (Fig. 31), though there is one great
difference. From beneath those of the Earwig project two small leathery
pieces which are absent in the Beetle. These pieces are not, as one
might imagine, at the tips of the wings, but on the front margin, about
halfway down, and is indicated in the illustration by the shading
between the extremity of the wing-case and the crease-mark at _a_.
[Illustration: FIG. 38.--Earwig (male).]
From the illustration we may understand how the Earwig opens and closes
its wings. From the point _a_ veins, which are thickened about
halfway down, radiate to the hinder edge of the wing, and a little
beyond the thickening they are connected by a vein which runs parallel
with the hinder edge. These radiating veins are brought together, so
that there is a fan-like closing, like that of the Cockroach, but from
a different centre. The wing is then folded back at the place where the
veins are thickened, and then there is a second transverse fold at the
point _a_, so that the only part of the wing now visible is the
leathery patch, which projects beyond the wing-case when the wing is
tucked away.
It is not difficult to unfold the wing of a dead specimen, under water,
using a needle and fine brush. Mr. E. A. Butler[25] recommends a simple
but excellent plan for unfolding and preserving the wing, by gumming
it, with the upper surface downwards, to a piece of card, and gradually
unfolding it and fastening it down. This is not so easy as it may seem,
but with patience and perseverance success will be obtained; and a
similar method may be adopted with the wings of other Insects, which
may be mounted in this way without any trouble. Thus they may be easily
preserved for examination at a future time, or for comparison with the
wings of other Insects.
It is rather remarkable that an insect like the Common Earwig, which
very rarely takes to flight, should have such a complex method of
folding its wings. Dr. Sharp says that though the Earwig ‘is scarcely
surpassed in numbers by any British insect, yet it is rarely seen on
the wing. It is probable that the majority of individuals of this
species may never make use of their organs of flight, or go through the
complex process of folding and unfolding them.’
Let us choose our next example from the Leaping Orthop´tera. They may
be distinguished at a glance from their relatives that run, but do not
leap, by the peculiar structure of the third pair of legs. These are
much longer and stouter than the other two pairs, and the thigh is very
muscular. This insect is a very good type of the family Locus´tidae, to
which, however, none of the insects popularly called ‘locusts’ belong.
They are included in another family (_Acridi´idae_), where the
common British Grasshoppers are also placed. The Locustids and the true
locusts may be distinguished by the difference in their antennae: in
the latter these organs are short, in the former they are very long and
delicate.
The Great Green Grasshopper (_Locus´ta viridis´sima_) (Fig. 39) is
fairly common all over the country, but often escapes observation from
the fact that its hue corresponds so nearly to that of the foliage on
or among which it lives. One specimen taken in a Devonshire lane gave
me a great deal of trouble before it was secured and transferred to
a small tube. It was perched on a leaf when I first saw it, and as I
approached it leaped away. Though I was certain it had not gone far,
it was some little time before I discovered it, and got near enough
to grasp leaf and insect, in time to prevent the latter from taking
another jump.
This insect may be kept alive in confinement for a considerable time,
and will do fairly well on a diet of leaves and fruit, though it will
not refuse an occasional meal of flesh. Dr. Sharp says that a specimen
in confinement ‘mastered a humble-bee, extracted with its mandibles
the honey-bag, and ate this dainty, leaving the other parts of the
bee untouched.’ It is said that if two be placed together in a box
they will fight most desperately, and that the victor will make a meal
off the body of its victim. De Geer witnessed a case of this kind in
a closely allied species that is found in Sweden. Its specific name
signifies ‘wart-eater,’ and commemorates the fact that the peasants
incite these insects to bite their warts, firmly believing that warts
once bitten speedily disappear, and do not grow again. Westwood says
that one of these insects actually devoured part of its own leg that
had been broken off accidentally. When the creature was seen at night
the detached leg was whole; in the morning about half of it had been
eaten.
[Illustration: FIG. 39.--Great Green Grasshopper
(female).]
It is well to get specimens of male and female insects. We shall
require the former in order to examine the sound-producing apparatus,
which the females do not possess; and the latter for the sake of the
ovipositor--a long scimitar-like organ by means of which the eggs are
deposited. Let us take the female first. The length, including the
ovipositor, is a little under two inches, and the antennae will measure
about as much more. The wing-cases do not lie flat upon the back, as do
those of the Cockroach, but in a slanting position, like the sides of
a roof, forming a ridge in the centre. The head is not bent back, as
in the Cockroach, nor does it project in front, as in the Beetles, but
the front is almost vertical. The armature of the mouth is strong, and
of the same pattern as that of the Cockroach. The hood--so the upper
covering of the thorax is called--is of a peculiar shape, somewhat like
that of a saddle. The wing-cases and wings, with their folding, will
offer little difficulty. Next we may examine the cerci, and contrast
them with those of the Cockroach and with the forceps of the Earwig.
Last of all, the ovipositor must be examined, and its structure made
out, so far as the means at our command will allow.
Apparatus of this kind for placing eggs in positions favourable to
their development is by no means confined to these insects, for
examples may be found in other Orders. Sirex, the so-called Tailed
Wasp, has a long straight one, which is often supposed to be a sting,
and the insect itself is not unfrequently taken for a gigantic wasp or
hornet.
When the ovipositor of our subject is looked at with the unassisted
eye, it appears to consist of two curved blades placed side by side,
with an internal groove on each. The apparatus, however, is not quite
so simple: it is made up of six chitinous rods, of which four--the two
above, and the two central ones--are developed from the ninth segment
of the abdomen, while the two lower ones spring from the eighth. It is
not difficult to test these statements. Specimens are plentiful; and as
the ovipositor in this insect is large, and easily broken up into its
component parts, it may well serve as an introduction to the study of
these organs in other Insects--the Saw-flies, for example.
When the insect is about to deposit her eggs, she selects a spot where
the soil is light, and bending the ovipositor nearly at a right angle
to her body, thrusts it into the ground as far as possible. Then, by
a muscular effort, the plates of the ovipositor are separated, and
several eggs travel down the passage formed by the central pair of rods
into the hole. This is repeated time after time, till the operation of
egg-laying is completed. This takes place in the autumn, and the young
emerge from the eggs in the spring. When they come out they are tiny
copies of the adults; but they do not acquire wings till after several
months. The ovipositor of the female appears after the second moult,
and till this organ is developed no difference is apparent between the
young insects.
The chief interest of the male insect lies in its wings, for the first
pair (the _teg´mina_) are the organs with which it produces its
‘love-songs.’ Kirby comments on the fact that Lichtenstein, in the
_Linnaean Transactions_ (iv. 51), ‘draws attention to the eye-like
area in the right wing-case of the males of this genus,’ adding that
that author seemed ‘not to be aware that De Geer had noticed it before
him, as a sexual character; and also, with good reason, supposed that
it assists these animals in the sounds they produce.’
This is how De Geer (_Mémoires_, iii. 429) describes the
sound-producing apparatus of the Great Green Grasshopper: ‘In our
male grasshoppers, in that part of the right elytron which is folded
horizontally over the trunk, there is a round plate of very fine
transparent membrane, resembling a little mirror or piece of talc, of
the tension of a drum. This membrane is surrounded by a strong and
prominent nervure, and is concealed under the fold of the left elytron,
which has also several prominent nervures answering to the margin of
the membrane or ocellus. There is every reason to believe that the
brisk movement with which the grasshopper rubs these nervures against
each other produces a vibration in the membrane, augmenting the sound.
The males in question sing continually in the hedges in the months of
July and August, especially towards sunset, and part of the night. When
any one approaches they immediately cease their “song.”’
It is probably unnecessary to do more than remark that the noises made
by Insects do not correspond to the voices of the higher animals. ‘For
no insect, like the larger animals, uses its mouth for utterance of
any kind: in this respect they are all perfectly mute; and, though
incessantly noisy, are everlastingly silent[26].’
Our plan with these wings is to first verify the fact of their bearing
these talc-like spots, the serrated nervures on the right and the
rudimentary file on the left elytron. The sound is produced by rubbing
the base of the left elytron against that of the right. A recent author
compares this insect to a fiddler, and says that the left tegmen is the
bow and the right the fiddle.
The last point to examine is the ear. It seems strange to say that
these insects have ears in their legs; but though some of the older
entomologists regarded these structures in the tibiae of the first pair
of legs as nothing more than resonators or sound-boards to intensify
their chirping, there is no doubt that they are really organs of
hearing. Much interesting information on this subject will be found in
Sir John Lubbock’s _Senses of Animals_.
[Illustration:
FIG. 40.--Tibial ear of Great Green Grasshopper.]
These oval patches are plainly distinguishable by the unassisted eye,
and correspond in function to the tympanum or drum of the human ear.
The air-supply to the tibiae is distinct from that of the rest of the
body, and is derived from a large orifice on each side of the first
segment of the thorax. These orifices may be seen by removing the
‘hood.’ Indeed, they cannot escape observation. From these orifices an
air-tube passes to each leg, dividing into two branches in the tibia
and reuniting below the drums.
Dr. Sharp[27] says that ‘although the tibial ears of the Locus´tidae
are very perfect organs, there is great difficulty in deciding on the
exact nature of their functions. They would appear to be admirably
adapted to determine the precise locality from which a sound proceeds
... for the legs can be moved in the freest manner in every direction,
so as to bring the drum into the most direct line of the vibrations.
But as to what kinds of vibrations may be perceived, and the manner
in which they may be transmitted to the nerves, there is but little
evidence.’
The next Order from which we shall choose examples will be the
Hemip´tera, containing the Land and Water Bugs and some other forms.
Our chief concern, however, is with the Water Bugs. In this Order the
metamorphosis is incomplete; the mouth is adapted for sucking the
juices of plants and animals; and there are usually four wings. In the
Land and Water Bugs, part of the fore wings is harder than the hind
wings; in the other winged members of the Order both pairs of wings are
membranous. The front wings are called hemel´ytra or halfel´ytra, to
distinguish them from the el´ytra or wing-cases of Beetles, which are
chitinous throughout. Fig. 41 shows the hemel´ytron and hind wing of a
Land Bug, and the names given to the different parts of the front wing.
[Illustration: FIG. 41.--A Land Bug (magnified).
_a_, corium; _b_, clavus; _c_, membrane.]
The Water Scorpion (_Nepa cine´rea_) is not difficult to procure,
or to keep in confinement when it is caught. It would be straining
language to call it a handsome creature, yet it well deserves careful
study, on account of the wonderful modification of the first pair of
legs, and it is from the resemblance of these to the pedipalps of the
scorpion that the insect derives its popular name. Its length is about
an inch and a quarter, from the tip of the beak, or rostrum, to the end
of the breathing-tube. Its greatest width is a little over a quarter of
an inch (Fig. 42). The general hue harmonizes well with the mud, but
the upper surface of the abdomen is a warm red, ‘and is thick set with
hair, so as to afford a very agreeable sight.’
[Illustration: FIG. 42.--Water Scorpion.]
It is extremely common in shallow pools, and its favourite haunt is
near the shore, where it will lie, almost buried in the mud, with its
raptorial legs elevated, ready to seize on any passing insect, and its
breathing-tube just pushed through the surface-film. I learnt this
habit of the insect on the first occasion on which I tried to collect
specimens of it. I had been told that a certain piece of water swarmed
with Water Scorpions. This, I afterwards found, was quite correct;
but though I worked the pond from end to end, a single specimen was
all that rewarded my labour. Whilst transferring the insect from the
net-tube to the bottle for transport, a stranger joined me, and kindly
volunteered his assistance. He had no collecting tackle, but in about
a quarter of an hour he brought at least a dozen good specimens in the
bottle he had borrowed.
It was natural to inquire to what his success was due. He told me that
it was his first attempt at collecting, but that just before joining
me he had noticed the ends of the breathing-tubes sticking out of the
water. This excited his curiosity, and on moving the mud with his
walking-stick, the insects were seen to crawl away slowly. When he
saw me transfer the Water Scorpion from the net-tube to the bottle, he
immediately recognized it. Then he courteously offered his help, for
which, of course, I was grateful.
We may keep the Water Scorpion alive for a considerable time in a small
bottle of water, in which is some growing weed. If we watch it moving
about, we shall see that the front legs are used for locomotion as well
as for seizing prey. Some authors doubt this. Any one may settle the
question for himself, if he will put one of these insects into a small
bottle with plenty of weed. Generally, however, the insect uses only
the second and third pairs for walking, the first pair being raised and
directed forward, with the tarsus bent at an angle (Fig. 42). Even when
it does use its front legs for locomotion, the action is not that of
walking; the insect employs these limbs to pull itself along in a sort
of ‘hand-over-hand’ fashion, but on a level surface it uses the first
pair in the same way as it does the other two pairs.
Its habit of burying itself in the mud may also be watched with very
little trouble. A common pudding-basin will make an excellent aquarium
for this purpose. The bottom is to be covered with garden mould and
vegetable _débris_, mixed with a few stones. The whole mass should
be arranged unevenly, so that when water is added it may not form one
sheet, but a series of small shallow pools. Very little duckweed will
serve to keep it sweet. It only remains to drop in the Water Scorpion.
Before long it will accommodate itself to its new surroundings, and so
bury itself that it will be no easy task to discover it.
An aquarium of the kind described stands at present on my
writing-table. Many have been the inquiries as to what kind of creature
lived therein; and more than one old hand at collecting has failed to
find the insect. It is always safe to look round the sides of the basin
for the breathing-tube; if it is not detected in this situation, a
glance along the surface of the tiny pools will probably show a break
in the film. The Water Scorpion will not be far off.
That the insect really does cover itself with mud may be demonstrated
by transferring it from the aquarium described to any shallow vessel,
and allowing a fine stream of water--say, from a dipping-tube--to fall
gently on it. The mud will be washed away, and in a few seconds will
settle at the bottom.
It is well to keep such an aquarium covered, for the Water Scorpion has
no mean power of flight. A circular plate of glass, which may be bought
for a few pence, makes the best cover, but a piece of fine muslin
fastened round the rim of the basin will do. Swammerdam says, ‘These
Water Scorpions live all the day in the water, out of which they rise
about the dusk of evening into the air, and so flying from place to
place, often betake themselves in quest of food to other waters.’ Then
follows a deduction which shows how far he was in advance of his time:
‘This affords us a satisfactory reason for the great number of insects
that immediately appear in the smallest collections of water, since
they may very well get thither when it is dark, so that the opinion
which ascribes to putrefaction the power of forming insects, &c., must,
by this instance of the Water Scorpion’s nocturnal transmigrations,
appear more and more frivolous and unnecessary.’
[Illustration:
FIG. 43.--_A._ Water Scorpion. _a_, rostrum;
_b_, wing-cases; _c_, wings; _d_ _d_,
second and third pairs of legs; _e_, raptorial legs (the
first pair); _f_, spine forming breathing-tube; _g_,
parasitic mite. _B._ Portion of an oviduct containing eggs
(magnified). _C._ An egg (magnified). _D._ Parasitic
mite. _a_, head; _b_, eyes; _c_, legs; _d_
_d_, legs (seen from under surface). (After Swammerdam.)]
No larva or other animal that is of any value should be kept in the
same aquarium with the Water Scorpion. Dr. Hill, who annotated the
English edition of Swammerdam, says, ‘There is not perhaps in all the
animal creation so outrageous or fierce a creature against those weaker
than itself as the Water Scorpion. It destroys, like the wolf among
sheep, twenty times as many as its hunger requires.’ The Rev. G. C.
Bateman placed one in a saucer with a tiny minnow; ‘but no sooner did
the little fish swim within reach of the fore-legs of the scorpion
than it was seized by them, and pressed against the hungry creature’s
rostrum.’ It seems to be particularly fond of Asellus, the water
woodlouse. I have often taken dead specimens of this crustacean, sucked
completely dry, from between the raptorial legs of the insect. One
specimen was so thoroughly cleaned out that it was mounted just as it
was, the only preparation being a brief soaking in spirit.
In examining the head the eyes may be readily distinguished, and on
pressing the rostrum or beak with a needle, the proboscis will be
forced out, just as one may force out the sting by pressing the abdomen
of a bee or a wasp. In this group the antennae are three-jointed and
concealed. When one begins to look for these organs he will probably
come to the conclusion that the concealment is highly effectual.
A very simple method of finding them in a spirit specimen is to take
the insect between the thumb and index finger of the left hand, holding
it up to the light in such fashion as to keep the first pair of legs
well clear of the head. Then, with a needle held in the right hand,
raise the thorax till it lies in the same plane as the body. Each
antenna lies in a groove beneath the eye. Gentle manipulation with the
needle will lift them out, so that they may be clearly seen, not only
with the hand magnifier, but with the unassisted eye. Or the insect may
be pinned down under water instead of being held in the hand, and the
antennae lifted or brushed out of the groove.
It will greatly simplify matters if, before attempting to raise the
wings, the fact is borne in mind that the tip of the right wing-case
lies over that of the left. It is perhaps as well to remove the
wing-case altogether by inserting a needle under it, and gently raising
it, using a little pressure in an outward direction. It will then be
quite time to raise the wing and to see the method of folding and
unfolding.
[Illustration: FIG. 44.--Raptorial leg of Water
Scorpion.]
In Fig. 44 we have a representation of the raptorial (front) leg
of this insect. This leg should be compared with the legs of other
Insects--not in pictures only, but in actual specimens--that we may see
how, while the general plan is preserved, different joints are modified
to suit the special function of this limb--that of taking prey. (See
also Fig. 43.)
The thigh (_f_) is the largest joint, for the obvious reason that
it contains the muscles that work the tibia and tarsus, which together
form a kind of knife-blade, shutting down into a groove in the thigh,
which may very well be compared to the handle of a pocket-knife. This
description, however, is not to be taken on trust. It is not enough
to read about the groove: we must see it for ourselves, raise the
‘knife-blade’ from the groove, and press it down again, and pass the
needle along the groove. If we examine the interior of the groove, we
shall find that there is a projection along the bottom, so that a cross
section would appear like this--W[image]. The inner portion of the
tibia is also grooved; so that when once the prey is seized by this
powerful limb, it has no chance of escape. The tarsus (_tar_)
is not clearly distinguished from the tibia (_tib_) in the
engraving, but it may be distinctly seen as a claw-like appendage in a
living or dead specimen.
The breathing-tube remains to be examined. It may be detached from the
body for more convenient manipulation. When this is done, the tube will
be seen to consist of two pieces, each grooved on the inner side and
set with hairs, which, as they interlock, prevent the entrance of water.
A somewhat similar arrangement occurs in the proboscis or tongue of
butterflies. There is perhaps a closer parallel in the antennae of
the masked crab, which, under certain conditions, form a kind of
breathing-tube, each antenna being joined to its fellow by the hairs
with which it is set.
There are two other Water Bugs which lend themselves to our purpose
very well. Each is popularly called Water Boatman, though that name is
better confined to Notonecta, because the insects of this genus ‘row
themselves about on their backs with their long feathered legs.’ In the
United States they are called Water Cicadae, from the shrill noise they
make, probably by rubbing the fore-legs together.
[Illustration: FIG. 45.--Water Boatman.]
In Fig. 45 the Water Boatman (_Notonec´ta glauca_) is represented
as seen from above--a position in which we shall rarely discover it,
if we keep it in a small aquarium. In Fig. 46 the same insect is shown
swimming on its back, or in the position it assumes when taking in a
supply of air. The end of the abdomen and the tips of the feet rest
against the surface-film; and at the slightest alarm a vigorous stroke
of the last pair of legs sends the insect to a place of safety. From
the way in which these insects habitually swim, Mouffet came to the
conclusion that it was probable men learned the art of swimming on
their backs from them.
[Illustration: FIG. 46.--Water Boatman swimming.]
Active as the Water Boatman is, it often falls a victim to the Water
Scorpion, if both are kept in the same aquarium. I learnt this fact by
experience, for having put two Water Boatmen into a small tank in which
was a Water Scorpion, I found both the former dead in the morning. It
was evident that their destroyer had had a good meal.
The only point to which attention need be called in examining the Water
Boatman is its method of taking in a supply of air. In looking at a
dead specimen we shall see a ridge or keel running down the middle of
the under side of the abdomen, and fringed with hair on each side.
A similar fringe runs along each side of the abdomen, thus forming
two passages along which the air taken in at the end of the body is
conveyed to the spiracles, the largest of which are on the thorax.
Corixa (Fig. 47) swims with its back uppermost, and when kept in the
aquarium may generally be seen foraging for small creatures--larvae or
worms--among the sediment at the bottom. Bateman, who kept a number
of these insects, says that he fed his specimens on garden worms and
pieces of raw meat. Mine have always foraged for themselves, and done
very well without feeding. They may often be seen to rub the short
fore-legs alternately across the front of the head, probably for the
purpose of producing a call-note. I have often watched them at this
practice, but have never been able to detect any sound. The defect is
evidently in my sense of hearing, for the sounds rest on undoubted
authority, and are coincident with the rubbing of the fore-legs across
the head.
[Illustration: FIG. 47.--Corixa, with wings expanded.]
Where sound-producing organs exist it is more than probable the
capacity for receiving sound-impressions also exists. Graber made some
interesting experiments to test the sense of hearing in Corixa. His
results are thus summarized by Sir John Lubbock[28]: ‘He placed some
Water Boatmen (Corixa) in a deep jar full of water, at the bottom
of which was a layer of mud. He dropped a stone on the mud, but the
insects, which were reposing quietly on some weeds, took no notice. He
then put a piece of glass on the mud, and dropped the stone on to it,
thus making a noise, though the disturbance of the water was the same.
The Water Boatmen, however, at once took to flight.’