an order of small parasitic insects. The mature animals are parasites on mammals and birds, feeding on their blood. Members of the order Aphaniptera are adapted for swift movement through hair or feathers. The body has flattened sides, and the head is usually rounded from the front, with a pair of simple eyes (some members of the order are blind). The elongated upper jaws are notched. The animal has piercing and sucking mouth parts. There are no wings. The hind pair of legs is especially strongly developed and serves for jumping. The body is covered with small hairs or bristles, which in places look like spines or teeth (some of the latter form combs, or ctenidia). The coloration of the body ranges from pale yellow to dark brown. The males are smaller than the females. The insects develop with full metamorphosis. They lay oval white eggs with blunt ends, approximately 0.5 mm long. A white, wormlike, legless larva whose body is covered with long setae hatches from the egg. The larvae feed on fecal matter of the adults, which has a high blood content, or on decaying organic remains. While pupating, the larva covers itself with a gossamer cocoon; the pupa is immobile and has the general body outline of the members of the order. For the human flea the egg phase is four to 12 days, the larval stage is eight to 100 days, the pupal stage is six to 220 days, and the entire life of the flea lasts up to 965 days.

Some species feed only on certain species of host animal. About 1,000 species are known. The human flea (Pulex irritans), the dog flea (Ctenocephalides canis), and the southern rat flea (Xenopsylla cheopis) are notable among species that harm man and animals; the alacurt (Vermipsylla alacurt) feeds on camels and sheep, and Echidnophaga gallinacea feeds on chickens and other animals.

The saliva of fleas has toxic, irritating properties. Rat fleas and those of the suslik (Ceratophyllus tesquorum), Mongolian bobak (Oropsylla silantiewi), and other animals are carriers of the plague among rodents and from rodents to man. The fleas of rats, mice (Leptopsylla musculi), dogs, and other animals transmit rickettsias, the causative agents of rat typhus. Dog and rat fleas are the intermediate hosts for the double-pored dog tapeworm {Dipylidium caninum). Measures for combating fleas include keeping dwellings clean, washing floors with a 2–5 percent soapsuds-carbolic solution, wiping corners with kerosene, spraying with pyrethrum or other insecticides, cleaning the bedding of dogs and cats, and puttying over cracks in the floor.