Fleas are the insects forming the order Siphonaptera. They are wingless, with mouthparts adapted for piercing skin and sucking blood. Fleas are external parasites, living by hematophagy off the blood of mammals and birds.
Some flea species include:
• Cat flea (Ctenocephalidesfelis)
• Dog flea (Ctenocephalidescanis)
• Human flea (Pulexirritans)
• Moorhen flea (Dasypsyllusgallinulae)
• Northern rat flea (Nosopsyllusfasciatus)
• Oriental rat flea (Xenopsyllacheopis)
Over 2,000 species have been described worldwide.
Life cycle and habitat
Fleas are holometabolous insects, going through the four life cycle stages of egg, larva, pupa, and imago (adult). Adult fleas must feed on blood before they can become capable of reproduction. Flea populations are evenly distributed, with about 50% eggs, 35% larvae, 10% pupae, and 5% adults.
The flea life cycle begins when the female lays after feeding. 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. In laboratory studies, some dietary diversity seems necessary for proper larval development. Blood only diets allow only 12% of larvae to mature, whereas blood and yeast or dog chow diets allow almost all larvae to mature.  They are blind and avoid sunlight, keeping to dark places like sand, cracks and crevices, and bedding.
Given an adequate supply of food, larvae will pupate and weave a silken cocoon within 1–2 weeks after 3 larval stages. After another week or two, the adult flea is fully developed and ready to emerge from the cocoon. They may 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. Their total life span can be as short as one year, but may be several years in ideal conditions. Female fleas can lay 5000 or more eggs over their life, allowing for phenomenal growth rates. Average 30–90 days.
A flea might live a year and a half under ideal conditions. These include the right temperature, food supply, and humidity. Generally speaking, an adult flea only lives for 2 or 3 months. Without a host for food a flea’s life might be as short as a few days. With ample food supply, the adult flea will often live up to 100 days.
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 21 °C to 30 °C (70 °F to 85 °F) and optimum humidity is 70%.
Adult female rabbit fleas, Spilopsylluscuniculi, can detect the changing levels of cortisol and corticosterone hormones in the rabbit’s blood that indicate it is getting close to giving birth. This triggers sexual maturity in the fleas and they start producing eggs. As soon as the baby rabbits are born, the fleas make their way down to them and once on board they start feeding, mating, and laying eggs. After 12 days, the adult fleas make their way back to the mother. They complete this mini-migration every time she gives birth