Fleas are wingless insects, with mouthparts adapted for piercing skin and sucking blood. Fleas are external parasites, living by hematophagy off the blood of mammals (including bats and humans) and birds.
Fleas are wingless insects 1/16 to 1/8-inch long that are agile, usually dark colored, with mouth-parts adapted to feeding on the blood of their hosts. Their legs are long, the hind pair well adapted for jumping. A flea can jump vertically up to 7 inches and horizontally up to 13 inches. This is around 200 times their own body length, making the flea one of the best jumpers of all known animals relative to their body size.
The flea body is hard, polished, and covered with many hairs and short spines directed backward, which also assist its movements on the host. The tough body is able to withstand great pressure, likely an adaptation to survive attempts to eliminate them by mashing or scratching. Even hard squeezing between the fingers is insufficient to kill a flea. Fleas can be drowned in water and may not survive direct contact with anti-flea pesticides.
Fleas lay tiny white, non-sticky, oval-shaped eggs. The larva is small, pale, has bristles covering its worm-like body, lacks eyes, and has mouthparts adapted to chewing. The larvae feed on various organic matter, especially the feces of mature fleas. The adult flea's diet consists solely of fresh blood. In the pupal phase, the larva is enclosed in a silken, debris-covered coccoon.
Fleas go through the four life cycle stages of egg, larva, pupa, and adult. The flea life cycle begins when the female lays eggs after feeding. Adult fleas must feed on blood before they can become capable of reproduction. Eggs are laid in batches of up to 20 or so, usually on the host itself, which means that the eggs can easily roll onto the ground. Because of this, areas where the host rests and sleeps become one of the primary habitats of eggs and developing fleas. The eggs take around two days to two weeks to hatch.
Flea larvae emerge from the eggs to feed on any available organic material such as dead insects, feces, and vegetable matter. They are blind and avoid sunlight, keeping to dark places like sand, cracks and crevices, and bedding. After another week or two, the adult flea is fully developed and ready to emerge from the cocoon. They may however remain resting during this period until they receive a signal that a host is near. Vibrations including sound, heat, and carbon dioxide are all stimuli indicating the probable presence of a host. Fleas are known to overwinter in the larval or pupal stages.
Once the flea reaches adulthood, its primary goal is to find blood and then to reproduce. Adult fleas only have about a week to find food once they emerge, but after that they can survive two months to a year between meals. Their total life cycle can be as short as two weeks, but may be several months in ideal conditions. Female fleas can lay 500 or more eggs over her life.
Newly emerged adult fleas live only about one week if a blood meal is not obtained. However, completely developed adult fleas can live for several months without eating, so long as they do not emerge from their puparia. Optimum temperatures for the flea's life cycle are 70°F to 85°F and 70% humidity.