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The human flea (''Pulex irritans'') is a cosmopolitan flea species that has, in spite of the common name, a wide host spectrum. It is one of six species in the genus ''Pulex''; the other five are all confined to the Nearctic and Neotropical regions. The species is thought to have originated in South America, where its original host may have been the guinea pig or peccary. ==Morphology and behavior== ''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 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Human flea」の詳細全文を読む スポンサード リンク
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