Fleas are parasites that feed on the blood of any warm-blooded body. Cat fleas are the most common domestic flea, but dog fleas, human fleas and oriental rat fleas can also be found. Fleas do not fly. Instead, they use their powerful legs to jump onto a passing host. Controlling and/or exterminating fleas can eliminate an infestation. Flea bites can result in painful, itchy red bumps. Fleas are also the most common transmitter of the rare bubonic plague.