Fleas are an external parasite that feed on the blood of animals and humans. Although they are often found on dogs and cats, they will also seek a meal off an unknowing rat or other animal. Within just two days of reaching adulthood, fleas feed with tube-like mouth-parts adapted to feeding on their host. At about 1/8" inch long, these tiny pests can jump up to 13 inches horizontally. They can be identified by their flat, brownish bodies. Their larvae is pale whitish in color and has a wormlike body.