Flea, a tiny, wingless insect. It is a household and barnyard pest, and a parasite that carries disease. Adult fleas, both male and female, live in the fur and hair of mammals and the feathers of birds, and feed exclusively on their blood. Their powerful sense of smell leads fleas to their victims.

A flea may be from one-tenth to nearly one-fourth of an inch (2.5 to 6 mm) long, depending on the species. Its body is very narrow from side to side, enabling the flea to glide between the hairs or feathers of its host. Backward-pointing bristles make a flea hard to dislodge. The body is covered with very tough skin, which allows fleas to withstand enormous amounts of pressure and makes them hard to kill. The flea's abdomen, which stores blood, is much larger than its head. The mouth parts are adapted to puncturing and sucking. A flea bite may cause a severe rash, soreness, or blisters. Fleas can survive for several months without feeding.

The flea'sThe flea's abdomen, which stores blood, is much larger than its head.

The specialized tissues of its hind legs can propel a flea from 50 to 150 times its body length. A broad-jump of nearly 13 inches (33 cm) and a vertical leap of 7 ¾ inches (19.7 cm) have been recorded. As a curiosity, fleas are sometimes exhibited at flea circuses where they perform such acts as pulling tiny wagons.

The flea'sThe flea's hind legs enable them to make impressive leaps.

The female flea lays eggs on its host. The eggs drop into the host's sleeping place or surroundings. Bristly, wormlike larvae emerge from the eggs. The larvae, which are not parasitic, feed on specks of organic matter, and then spin cocoons within which they change into adults.

Kinds of Fleas

There are nearly 2,400 species and subspecies of fleas. The Oriental rat flea and the European rat flea can transmit diseases from infected rats to humans. These diseases include bubonic plague—the “Black Death” of the 14th century—and murine typhus, which was common in the southeastern United States during 1944-50.

The sticktight, or chicken flea, is a serious pest of poultry. The human flea, more common in Europe than in the United States, often infests pigs, but also transmits diseases to humans. The dog flea and the cat flea, which may live upon each other's favorite hosts, and temporarily on rats and humans, are household pests. Dog fleas can transmit the eggs of dog tapeworms to dogs, cats, and humans. Dog and cat fleas may be controlled with powders, sprays, and shampoos containing insecticides. Flea collars—collars treated with insecticides—are rarely effective. Dogs and cats can be given pills containing the drug lufenuron, which enters the blood and is ingested by the fleas. The drug keeps eggs laid by the fleas from hatching, thereby preventing the fleas from reproducing.

Fleas make up the order Siphonaptera. The Oriental rat flea is Xenopsylla cheopis; European rat flea, Nosopsyllus fasciatus; human flea, Pulex irritans; dog flea, Ctenocephalides canis; cat flea, C. felis; chicken flea, Echidnophaga gallinacea.