The fleas are a small order of tiny, wingless, brown to black insects which live in the fur or plumage of mammals and birds, where they feed on blood.

Fleas are easily recognizable by the laterally compressed body, which usually is equipped with one or more combs of strong setae on head or thorax. The legs are strong and adapted for jumping. Fleas have complete metamorphosis, and the slender, blind and legless larvae feed on organic debris in the nests and burrows of the host. Some fleas are host specific, but most can have multiple hosts. Fleas can cause allergic reactions in humans, and can transfer some diseases from animals to humans, most notably salmonella, tularemia, and the notorious plague bacterium, Yersinia pestis.