Fleas

Fleas have a laterally compressed body, a tough, smooth cuticle with many backward-projecting bristles, and relatively long legs. The mouth parts of fleas include stylets that are used to pierce the skin of the host animal, so that a blood meal can be obtained by sucking.

Fleas have a life cycle characterized by four developmental stages: egg, larva, pupa, and adult. The eggs are usually laid close to the body of the host in a place where the host commonly occurs, for example, on the ground, in a bird or mammal nest, or in carpets or soft furniture in homes. Larval fleas have chewing mouth parts and feed on organic debris and the feces of adult fleas, while adults require meals of bird or mammal blood.

Fleas commonly spend a great deal of time off their hosts, for example, in vegetation or on the ground. They can generally survive for a long time without feeding, while waiting for a suitable opportunity to parasitize a host animal. Fleas are wingless, but they walk well and actively travel over the body of their hosts, and between hosts as well.

Fleas are well known for their jumping ability, with their hind legs providing the propulsive mechanism. As a defensive measure, a flea can propel itself many times its body length through the air. The human flea (Pulex irritans), for example, can jump as high as 7.9 in (20 cm) and as far as 15 in (38 cm), compared with a body length of only a few millimeters.