Human flea

Pulex irritans is a holometabolous insect with a four-part lifecycle consisting of eggs, larvae, pupae, and adults. Eggs are shed by the female in the environment and hatch into larvae in about 3–4 days. Larvae feed on organic debris in the environment. Larvae eventually form pupae, which are in cocoons that are often covered with debris from the environment (sand, pebbles, etc.). The larval and pupal stages are completed in about 3–4 weeks when the adults hatch from pupae, then must seek out a warm-blooded host for blood meals.

The flea eggs are about 0.5 mm in length. They are oval-shaped and pearly white in color. Eggs are often laid on the body of the host, but they often fall off in many different places. The larvae are about 0.6 mm in length. They are creamy white or yellow in color. Larvae have 13 segments with bristles on each segment. The larvae feed on a variety of organic debris. The pupa are around 4 x 2 mm. After undergoing three separate molts, the larvae pupate, then emerge as adults. If conditions are unfavorable, a cocooned flea can remain dormant for up to a year in the pupal phase. The adults are roughly 1.5 to 4 mm in length and are laterally flattened. They are dark brown in color, are wingless, and have piercing-sucking mouthparts that aid in feeding on the host's blood. Both genal and pronotal combs are absent and the adult flea has a rounded head. Most fleas are distributed in the egg, larval, or pupal stages.

Common treatments include body shaving and medicated shampoos and combing. When preventing fleas, it is important to treat both the host and the environment. Household pets should be treated to prevent being infested. Carpets, and other floor surfaces, should be shampooed and vacuumed regularly to prevent fleas. When dealing with an infestation, bedding and clothing that may have been exposed should be washed thoroughly in hot water and kept away from other materials that have not been exposed. In extreme cases, extermination by a professional is necessary.

Pulex irritans originated in Central and South America, where it evolved with only one host.[4] Despite the origins of P. irritans, it is now a cosmopolitan species, most likely due to the fur trade after the 18th century, and pet transport in more recent decades.[4][5] Due to the cosmopolitan distribution of this group, research has been conducted to show that P. irritans individuals, when sampled from Spain and Argentina, only showed significant differences when comparing molecular data.[6] The use of morphometric data, which is often the method for flea identification, showed no significant levels of divergence between the two populations. Combining both morphological and molecular data has identified the possibility of cryptic species. This indicates a need to reconsider taxonomic classifications of these fleas. Studies in Europe and the Mediterranean also found this to be true. Human and cat fleas from Europe and the Mediterranean were studied and show such great variation within their own species that their taxonomy should be reevaluated based on mitochondrial gene heterogeneity.[5]

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