Fleas bite because they feed on the blood of animals and humans. Fleas feed on domestic and wild animals. A female flea is capable of consuming up to 15 times her weight in blood each day, according to AgriLife Extension.
Commonly, fleas bite the legs and feet of humans in infested homes. Flea bites may appear as small reddish bumps or may cause an allergic reaction in some people. There are many different types of fleas, including the dog flea, rat flea and human flea, according to AgriLife Extension. Fleas that bite wild animals and then people may transmit dangerous diseases, such as plague.