THE FLEA (_Pulex irritans_)
Marke but this flea, and marke in this,
How little that which thou denyst me is;
It sucked me first, and now sucks thee,
And in this flea our two bloods mingled bee.
(DR. DONNE.)
THE fact, now fully established, that the bubonic plague is conveyed to
man from infected rats, or from infected men to healthy men, by fleas
has taken that wingless insect out of the category of those animals
which it is indelicate to discuss.
No doubt, as Mr. Dombey says, ‘_Nature is on the whole a very
respectable institution_’; but there are times when she presents
herself in a form not to be talked about, and until a few years ago the
flea was such a form. Hence, few but specialists have any clear idea
either of the structure or of the life-history or of the habits—save
one—of the flea.
[Illustration: FIG. 6.—_Pulex irritans_, female. The legs of the left
side only are shown. Enlarged. (After a drawing by A. Dampf.)]
Fleas are temporarily parasitic on many mammals and birds, but some
mammals and some birds are much freer from fleas than others. As the
flea is only on its host for part of the time, it has to put in the
rest of its existence in some other place, and this, in the case of
the human flea, is usually the floor, and in the case of bird-fleas
the nest; from these habitats they can easily regain their hosts
when the latter retire to rest. But large numbers of Ungulates—deer,
cattle, antelopes, goats, wild boars—sleep in different places each
recurrent night, and to this is probably due the fact that, with the
exception of two rare species—one taken in Northern China and the other
in Transcaucasia—the Ungulates have furnished descriptive science
with no fleas at all. Both of these Ungulate fleas are allied to the
burrowing-fleas or ‘chigoes.’
I know none of my readers will believe me when I say that the same
is true of monkeys; but I do this on the undoubted authority of Mr.
Harold Russell, who has recently published a charming little monograph
on these lively little creatures. Monkeys in nature are cleanly in
their habits; and although in confinement occasionally a human flea
attacks them, and although occasionally a chigo bores into the toes of
a gorilla or chimpanzee, ‘speaking generally, it may be said that no
fleas have been found truly parasitic on monkeys.’ Whatever the monkeys
are looking for, it is not fleas. What they seek and find is in effect
little scabs of scurf which are made palatable to their taste by a
certain sour sweat.
As a rule, each host has its own species of flea; but though for the
most part _Pulex irritans_ is confined to man it is occasionally
found on cats and dogs, whilst conversely the cat- and dog-fleas
(_Ctenocephalus felis_ and _Ct. canis_) from time to time attack man.
The bite of the flea is accompanied by the injection of the secretions
of the so-called salivary glands of the insect, and this secretion
retards the coagulation of the victim’s blood, stimulates the
blood-flow, and sets up the irritation we have all felt.
It is only a few years ago that the spread of bubonic plague was
associated first with rats, and then with rat-fleas; and at once it
became of enormous importance to know which of the numerous species
of rat-flea would attack human beings. The Hon. Charles Rothschild,
who has accumulated a most splendid collection of preserved fleas
in the museum at Tring, had some years ago differentiated from an
undifferentiated assemblage of fleas a species first collected in
Egypt, but now known to be the commonest rat-flea in all tropical
and sub-tropical countries. This species _Xenopsylla cheopis_—and to
a lesser extent _Ceratophyllus fasciatus_—unfortunately infests and
bites man. If they should have fed upon a plague-infected rat and
subsequently bite man, their bites communicate bubonic plague to human
beings. Plague—the Old English ‘Black Death’—is a real peril in our
armies now operating in Asia and in certain parts of Africa.
Just as some fleas attack one species of mammal or bird and avoid
closely allied species, so the human flea has its favourites and
its aversions. There is a Turkish proverb which says ‘an Englishman
will burn a bed to catch a flea,’ and those who suffer severely from
fleabites would certainly do so. The courage of the Turk in facing
the flea, and even worse dangers, may be, as the schoolboy wrote,
‘explained by the fact that a man with more than one wife is more
willing to face death than if he had only one.’ But there are persons
even a flea will not bite. Mr. Russell has reminded us in his Preface
of the distinguished French lady who remarked, ‘Quant à moi ce n’est
pas la morsure, c’est la promenade!’
[Illustration: FIG. 7.—Larva of _Pulex irritans_. _C.f._ frontal horn;
_d_, antenna. Enlarged. (After Brumpt.)]
There are one or two structural features in a flea which are peculiar:
the most remarkable being that, unlike most other insects, it is much
taller than it is broad. As a rule, insects—such as a cockroach, the
bed-bug, or a stag-beetle—are like skates, broader than they are thick,
but the flea has a laterally compressed shape, like a mackerel or a
herring. Then, again, the three segments or rings which come after the
head are not fused into a solid cuirass or thorax as they are in the
fly or the bee, but they are movable one on the other. Finally, it
is usual in insects for the first joint of the leg to be pressed up
against and fused with those segments of the body that bear them; but
in the flea not only is this joint quite free, but the body-segment
gives off a projection which stretches out to bear the leg. Thus the
legs seem, unless carefully studied, to have an extra joint and to
be—as indeed it is—of unusual length. They certainly possess unusual
powers of jumping—as Gascoigne, a sixteenth-century poet (1540–78)
writes, ‘The hungry fleas which frisk so fresh.’
The male, as is so often the case amongst the Invertebrata, is much
smaller than the female. The latter lays at a time from one to
five minute, sticky, white eggs, one-fortieth of an inch long by
one-sixtieth broad. They are not laid on the host, but in crevices
between boards, on the floor, between cracks in the wainscoting, or
at the bottom of a dog-kennel or in birds’ nests. Mr. Butler recalls
the case of a gentleman who collected on four successive mornings
sixty-two, seventy-eight, sixty-seven, and seventy-seven cat-fleas’
eggs from the cloth his cat had slept upon. Altogether 284 eggs in four
nights! The date of hatching varies very much with the temperature.
_Pulex irritans_ takes half as long again—six weeks instead of four—to
become an adult imago in winter than it does in summer. But in India
the dog-flea will complete its cycle in a fortnight.
[Illustration: FIG. 8.—Pupa of flea. (After Westwood.)]
When it does emerge from the egg the larva is seen to be a whitish
segmented little grub without any limbs, but with plenty of bristles
which help it to move about; this it does very actively. There are two
small antennae and a pair of powerful jaws, for the larva does not take
liquid food, but eats any scraps of solid organic matter which it comes
across: dead flies and gnats are readily devoured. The larva casts its
skin several times, though exactly how often it moults seems still
uncertain.
After about twelve days of larval existence it spins itself a little
cocoon in some sheltered crevice, and turns into a whitish inert
chrysalis or pupa. During its pupal existence it takes, of course, no
food, but it grows gradually darker, and after undergoing a tremendous
internal change, breaking down its old tissues and building up new
ones, the chrysalis-case cracks and the adult flea jumps out into the
world.
There are many superstitions about fleas. March 1st is in some way
connected with them, and in the south of England the house-doors are
in some villages closed on that day under the belief that this will
render the building immune for the following twelve months. The most
successful insecticide is said to be prepared from _Pyrethrum_, which
is grown in the Near East in large quantities for this purpose. But the
Austrians, the Serbians, and the Montenegrins are fighting over the
chief world-supply of this plant—possibly without knowing what they
are doing—and ‘_Insektenpulver_’ is bound to go up in price. Wormwood
(_Artemisia_) is also recommended.
While wormwood hath seed, get a handfull or twaine,
To save against March, to make flea to refraine;
When chambere is swept and wormwood is strowne,
No flea for his life dare abide to be known.
(=TUSSER.=)
The author of ‘A Thousand Notable Things’ suggests the following plan,
but, so far, I have not met anyone who has tried it: ‘If you mark where
your right foot doth stand at the first time that you do hear the
cuckow, and then grave or take up the earth under the same; wheresoever
the same is sprinkled about, there will no fleas breed. I know it hath
proved true.’
Plastering a floor with cow-dung is a common practice in South Africa,
and seems to be an efficacious means of keeping down fleas. Dr. R.
J. Drummond tells me that all natives of India and Ceylon spread an
emulsion of cow-dung in hot-water over the floors and the walls of
their dwellings to keep out fleas. This has been done from immemorial
times, and is effective. The efficacy of the emulsion in keeping fleas
away has been doubted, and so I am glad to quote a few lines from a
kind letter sent me by Dr. P. A. Nightingale of Victoria, Southern
Rhodesia, which put the matter in a happy light:—
I think the correct facts are these: the floors of certain houses,
huts, &c., throughout the South African veld are made of ant-heap
earth, moistened and beaten hard and flat with sticks. This floor
is then smeared at regular intervals—say, every ten days—with fresh
cow-dung, when the room becomes fresh and sweet (!) and free from
insects.
However, before the smearing can be done it is necessary to turn all
the furniture out of the room and to sweep it thoroughly; after the
smearing, the doors and windows are left open for drying purposes.
Hence, I think that the absence of fleas in such quarters is really
due to general cleanliness, sunlight, and fresh air, and not to any
special virtue in the cow-dung.
I am, however, sure that the smearing of the floor at frequent
intervals _does_ keep many pests down by filling up, and temporarily
sealing, the numerous cracks in the floor where fleas, &c., reside
and breed in vast numbers.
Huts—especially unused ones—not smeared for many weeks contain
(approximately) several thousands of fleas, white ants, centipedes,
and scorpions to the square inch, when the only treatment is to
cleanse the walls and floor with cyanide solution, or burn the whole
place down.
[Illustration: FIG. 9.—_Ceratophyllus gallinulae._ Male (above) and
female (below). Drawn to scale and both highly magnified. These
specimens, taken from a grouse, are of the same genus as one of the
plague-conveying fleas.]
From long experience, I am very nearly insect proof; but cannot stand
the myriads of fleas I occasionally have to sleep with in a hut of
the above description—especially just before the rains set in, when
additional veld pests come into the huts for shelter.
We must, in the long run, treat fleas seriously. Although the _Pulex
irritans_ is a very common insect, the greatest living authority
on fleas tells me it has never been accurately drawn. We have
Blake’s ‘ghost of a flea’; but what did Blake know of entomology? In
distinguishing one flea from another—fleas which may attack man and
fleas which have hitherto declined to do so—every hair, every bristle,
counts. Hence, I illustrate this article with accurate outlines of
certain fleas found on the grouse, and for whose accuracy I can vouch
(Fig. 9).
As I have said above, a certain rat-flea (_Xenopsylla cheopis_) and
another (_Ceratophyllus fasciatus_) undoubtedly convey the bacillus of
plague from rats and other Murinae to man and vice versa. The _Bacillus
pestis_ is unlikely to establish itself in the present war in Europe,
but _Quién sabe?_ The Black Death of 1349–51 was conveyed by fleas, and
so was Pepys’s Plague of 1665. Plague—flea-borne, we must remember—is
still endemic in places as near Europe as Tripoli, and in numerous
centres in Asia. Not a disease altogether to be neglected, since the
spread of war to the Near East, but still not very threatening in
Europe in the twentieth century.