Fleah, or flea, cognate with flee, to run away from, to take flight), a name typically applied to Pulex irritans, a well-known blood-sucking insect-parasite of man and other mammals, remarkable for its powers of leaping, and nearly cosmopolitan.
The human flea is considerably exceeded in size by certain other species found upon much smaller hosts; thus the European Hystrichopsylla talpae, a parasite of the mole, shrew and other small mammals, attains a length of 5z millimetres; another large species infests the Indian porcupine.
A B In Great Britain the flea beetles (Halticidae) are one of the most serious enemies; one of these, the turnip flea (Phyllotreta nemorum), has in some years, notably 1881, caused more than 500,00o loss in England and Scotland alone by eating the young seedling turnips, cabbage and other Cruciferae.
The " tobacco flea-beetle " (Epitrix parvula, Fabr.) is a small active beetle, the larvae of which attack the roots, while the adult beetles eat holes in the leaves.
The gad-fly (abu), the housefly (hai), the mosquito (ka), the flea (nonzi) and occasionally the bedbug (called by the Japanese kara-mushi because it is believed to be imported from China), are all fully represented, and the dragon-fly (tombO) presents itself in immense numbers at certain seasons.
The tsetse fly (Glossing morsitans) infests several districts; the sand-flea has been imported from the west coast.
His chapter on the flea, in which he not only describes its structure, but traces out the whole history of its metamorphoses from its first emergence from the egg, is full of interest - not so much for the exactness of his observations, as for its incidental revelation of the extraordinary ignorance then prevalent in regard to the origin and propagation of "this minute and despised creature," which some asserted to be produced from sand, others from dust, others from the dung of pigeons, and others from urine, but which he showed to be "endowed with as great perfection in its kind as any large animal," and proved to breed in the regular way of winged insects.
He even noted the fact that the pupa of the flea is sometimes attacked and fed upon by a mite - an observation which suggested the well.
What in California are known as " flea seeds " are oak-galls made by a species of Cynips; in August they become detached from the leaves that bear them, and are caused to jump by the spasmodic movements of the grub within the thin-walled gall-cavity."
Though this may dishearten the systematist, Scourfield (1900) reminds us that " It was in a water-flea that Metschni koff first saw the leucocytes (or phagocytes) trying to get rid of disease germs by swallowing them, and was so led to his epochmaking discovery of the part played by these minute amoeboid corpuscles in the animal body."
As to how they convey it from man to man the greatest probability is in favour of the flea as an intermediary.
Healthy rats contracted plague from infected rats when the only apparent means of communication between the two was the rat flea (pulex cheopis).
In 21 experiments out of 38, 55% of healthy rats living in flea-proof cages have contracted plague after receiving fleas collected from rats either dead or dying of septicaemic plague; consequently it is proved the rat flea can transmit plague from rat to rat.
Guinea-pigs set free in plague-infected houses become infected with the rat flea and develop plague in a certain percentage.
Fleas caught on plague-infected rats are able to infect rats placed in flea-proof cages.
It was also shown that animals may become infected through the faeces of a flea which has been fed on plague-infected rats.
The report also considers it proved that the bacillus pestis multiplies in the stomach of a flea and may remain a considerable time within its host.
(2) A flea can retain the plague bacilli alive for seven or eight days.
(4) The rat flea, when finding no rats, will attack man and it will also attack other animals.
From the little flea-like species, scarcely a tenth of an inch long, up to the great and rare but cosmopolitan Eurythenes gryllus, Lichtenstein, and the still larger Alicella gigantea, Chevreux, nearly half a foot long, captured by the prince of Monaco from a depth of 2936 fathoms, not one of these ubiquitous, uncountable hordes has ever been accused of assailing man.
The common small white butterfly of Europe (Pontia or Pieris rapae) is now established in North America; and the march of the jigger, or foot-infesting flea (Sarcopsylla penetrans) of tropical America, across Africa, has taken place in quite recent years.