Dog and Cat insecticide Fleas Fleas are small, wingless insects that live as external parasites on mammals and birds. About 16,000 species are known worldwide, including 250 species in North America. Fleas have distinctive, laterally flattened abdomens with many spines and bristles. They can easily slip between the feathers or hair of their hosts. Their bodies have tough skins, making them extremely difficult to kill.
Most fleas lay eggs in dirt or lint, or in their host's nest.
Some species attach eggs directly to the host's hair or feathers. It is interesting to note that cat flea females lay between 50-100 eggs, usually among cat's bedding, and a human flea female will lay approximately 500 eggs in her lifetime, which may be 18 months if well fed.