Fleas are from the order of Siphonaptera measuring 1.5 to 3.3 mm long. Their body parts are laterally compressed, agile, usually dark colored. They are wingless insects with tube-like mouth-parts adapted to feeding on the blood of their hosts. Their legs are long, the hind pair well adapted for jumping.
They are capable of around 200 times their own body length, making the flea one of the best jumpers of all known animals relative to body size. The tough body is able to withstand great pressure, likely an adaptation to survive attempts to eliminate them by mashing or scratching. Fleas attack a wide variety of warm-blooded vertebrates including dogs, cats, humans, chickens, rabbits, squirrels, rats, ferrets, and mice.
Fleas are a nuisance to their hosts, causing an itching sensation. Flea bites generally result in the formation of a slightly raised, swollen itching spot with a single puncture point at the center. The bites often appear in clusters or lines of two bites, and can remain itchy and inflamed for up to several weeks afterwards.