Fleas are small (1/16 to 1/8 inches long), agile and usually dark in color. Fleas are wingless insects whose mouthparts are adapted for piercing skin and sucking blood. Their legs are long and the hind pair is well adapted for jumping. In fact, the flea is one of the best jumpers of all known animals. Fleas can jump around 200 times their own body length! They can jump vertically up to seven inches and horizontally up to thirteen inches.
A flea's body is hard, polished and covered with many hairs and short spines directed backward. The flea's tough body is able to withstand great pressure, even hard squeezing between the fingers is normally insufficient to kill a flea. Adult fleas must feed on blood before they can become capable of reproduction. Eggs are laid in batches of up to 20 and take around two days to two weeks to hatch.
Some people and animals suffer allergic reactions to flea saliva resulting in rashes. 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. Fleas can also lead to hair loss as a result of frequent scratching and biting by the animal, and can cause anemia in extreme cases.