Fleas

Fleas are small, wingless insects with tube-like mouth-parts adapted to feeding on the blood of their hosts. Their legs are long and well adapted for jumping.  An adult flea, for example, can jump vertically up to 7 inches, making it one of the best jumpers (relative to body size) of all known animals.

It's body is hard, polished, and covered with hairs and short spines directed backward, a feature which assist its movements on the host through fur or clothing. The tough body of the flea is able to withstand great pressure, and even squeezing one between the fingers is usually insufficient to kill a flea. Fleas can be drowned in water or killed with anti-flea pesticides.

Fleas have four stages in their  life cycle, consisting of egg, larva, pupa, and adult.  Adult fleas must feed on blood before they can reproduce, and, not surprisingly, the flea life cycle begins when the female lays after feeding.
Eggs are laid in batches of up to 20, usually on the host itself, and because of this the areas where the host rests and sleeps become one of the primary habitats of eggs and developing fleas.