Insect guide > Fleas


Fleas(Order Siphonaptera.)
The insects of this order, comprising all of the true fleas, are ail contained in a single family, the Pulicidae. They are all wingless, the mouth-parts are formed for sucking, and the body is compressed from side to side. The antennae are short and thick, and are placed in depressions behind the simple unfaceted eyes. The metamorphosis is complete. They are the greatest jumpers known in nature. The fleas are like the mosquitoes, comparatively few in number of species, but very abundant in individuals, and well represent in structure the degraded form which is the result of a semi-parasitic life. They prey upon nearly all species of warm-blooded animals, some, and in fact most species of fleas, passing readily from one species of animal to another. Very many different kinds of birds are infested by Pulex avium, while Pulex serraticeps occurs all a over the world, infesting cats and dogs, both domestic and wild, upon the Egyptian Ichneumon and the common European pole-cat, the striped hyaena, the common hare, the raccoon, and it also bites human beings.

The food of flea larvae has been the subject of some discussion. The old statement that the female flea disgorges drops of blood upon which her young feed, seems true only to a small degree. Laboulbene, the famous French entomologist, at first believed that blood was necessary for the nourishment of the larvae, the reddish colored contents of the digestive tract making him think so, but he found that they would flourish and complete their metamorphoses in sweepings in which there was no trace of blood. He concluded that all that has been said about P. irritans (the human flea of Europe) nourishing its young on dried blood is very problematic. Mr. W.J. Simmons found flea larvae feeding upon a dust composed of fragments of cuticle, hairs, fibers, and pellets of dried blood, the last being probably the natural excreta of the fleas. The writer has fed them succesfully upon moist bread crumbs, and it is reasonably certain that they will feed upon the dust or minute particles of almost any kind of organic matter.

The minute, delicate, whitish eggs hatch into slender, worm- like larvae, which, when full-grown, spin delicate cocoons, and transform to pupae, from which issue the adults. Rather more than 100 species are known, of which about 30 have been found in the United States.

In the recent important and alarming indictments of certain species of insects as carriers and transmitters of certain human diseases, fleas have not escaped. Grassi considers that the cat and dog flea (P. serraticeps) is an intermediate host of Taenia (tape-worms), while Simon and others have brought forward some proof that certain fleas convey the germs of the bubonic plague from rats to human beings, and from one person to another.

A curious and aberrant flea is the so-called "chigoe" or chigger of tropical America (Sarcopsylla penetrans), not to be confused with the so-called chigger of Virginia and southward, which is the larva of a mite. The female of the chigoe, sometimes found in tropical Florida, and frequently brought to American southern seaports (New Orleans, Savannah and Charleston), buries the forepart of her body in the flesh of human beings, the abdomen becoming greatly distended and discharging a number of eggs.

Another species of the same genus (S. gallinacea), sometimes called the chicken flea, buries itself in the eyelids of domestic fowls in our southern states and in other parts of the world.

Life-History of the Cat and Dog Flea
(Pulex serraticeps Gervais.)
This insect, commonly known as the cat and dog flea, as stated above, occurs on a number of different animals, and in the northeastern United States at least is the common flea, which proves a pest in houses. The true human flea, so-called (P. irritans), seems to be very rare in the United States, although common enough in Europe, as travelers and those who have read Mark Twain's account of the "chamois" well know. The eggs of the cat and dog flea are deposited between the hairs of the infested animals, but are not fastened to them, so that when the animal moves about or lies down, large numbers of the eggs will be dislodged and drop to the ground or floor, or wherever the animal may be at the time. An easy way to collect them, therefore, is to lay a strip of cloth for the animal to sleep upon, and afterwards brush the cloth into a receptacle, in which the eggs will be found in numbers. The eggs hatch under favorable circumstances in from two to four days, and the young larvae, very slender and elongate, white in color, and of the structure shown in the accompanying figure, crawl into the floor cracks and feed upon the accumulated dust. They may be reared under observation, in saucers, between layers of blotting paper, with dust and bread crumbs. Specimens studied by Mr. Pergande, showed that the larva casts its first skin in from three to seven days, and its second skin in from three to four days. From seven to fourteen days after hatching, they began to spin a delicate silken cocoon, which, when completed, was almost transparent, except where it was covered with dust particles. In the cocoon the pupa, as shown in the accompanying figure, was formed and the insect remained in the pupal condition for four days. Thus an entire generation may be developed in about a fortnight, and since the adult female lays many eggs, it is not surprising that persons having cats or dogs about the house will frequently (and especially where the houses are closed during the summer, and the floors left unswept) find their domiciles overrun with thousands of these active, biting creatures.