There are more than 2000 species of trombiculid mites in many genera, but onlyabout 20 species commonly attack people. The family Trombiculidae has a more orless worldwide distribution, but the medically most important species, such asLeptotrombidium deliense, L. akamushi andL. fletcheri, which are vectors of scrub typhus(Orientia tsutsugamushi), are found in Asia, the Pacificregions and the northeast coast of Australia.

Other trombiculid mites in many parts of the world cause itching and a form ofdermatitis known as scrub itch, autumnal itch or trombidiosis. In northernEurope larvae of Neotrombicula autumnalis(harvest mites ) and in North America andparts of Central and South America larvae of Eutrombiculaalfreddugesi (red bugs ) commonlyattack people and cause considerable discomfort. Some authors place both thesespecies in the genus Trombicula.

External morphology

Adults and nymphs

Adults are small (1–2 mm), usually reddish, and covered dorsally and ventrallywith numerous feathered hairs giving them avelvety appearance. The four pairs of legs end in paired claws. The body isdistinctly constricted between the third and fourth pairs of legs, giving it anoutline resembling a figure of eight . Palps andmouthparts project in front of the body and are clearly visible (Fig. 19.1).

Nymphs resemble the adults but are smaller (0.5–1.0mm) and the body is lessdensely covered with feathered hairs.

Neither adults nor nymphs are of direct medicalimportance; they do not bite humans or animals but feed on small arthropods andtheir eggs. Only the larvae are parasitic and hence disease vectors.