Fleas are parasites that live on the exterior surface of a host animal. There are many different species of fleas, and each type of flea has a particular species of animal that it lives on. Fleas can be found all over the world wherever their hosts live.
Adult fleas live on the host animal, drinking blood from the host animal to survive. Fleas reproduce by laying large numbers of eggs. Some of the eggs remain on the host animal, and others fall off into the environment. The eggs hatch into worm-like larvae that eventually turn into adult fleas. If a flea developed in the environment instead of on a host animal, it searches for a host animal to inhabit. Most flea species seem to prefer living on rodents and similar animals because they maintain permanent dens, which are ideal environments for flea larval development.