Field Guide to Venomous and Medically Important Invertebrates ...

Larval chiggers actively crawl to the tips of vegetation such as grasses and wait for a host to
pass. Various rodents and other small mammals are the normal hosts of chiggers, but unwary
humans become hosts when they venture into chigger habitat without personal protection. Once
on the host, the larval chiggers move to an ideal feeding spot where they attach themselves
tightly to the skin. Contrary to popular belief, chiggers do not burrow into the skin or suck
blood. They pierce the skin (often around a hair follicle) to feed on lymph and dander and in the
process they introduce digestive enzymes into the host tissues. The chiggers then begin to feed
on the liquefied host tissues. Subsequently, and usually after the chigger has left the host, the
sourronding tissues to become inflamed and each bite has a characteristic red welt with a white,
hard central area. The rash and intense itching associated with chiggers therefore is an allergic
reaction to the mite's salivary secretions. Secondary infections ma result from scratching the bite
site. After becoming fully fed, the chigger drops from its host, goes into the ground and enters a
quiescent stage. In the fall of the year, it becomes a bright red adult that overwinters in that
stage.
Two genera of chigger mites, each containing many species, are of concern to deployed military
forces. They are Eutrombicula and Leptotrombidium. Chiggers in the genus Eutrombicula do
not transmit any known pathogens to people, but they can cause irritating bites, dermatitis and
severe itching when they feed on the unsuspecting host. They are widely distributed in the
Western Hemisphere, and Europe. By comparison chiggers in the genus Leptotrombidium are
the vectors of scrub typhus throughout Asia and portions of Australia. The bite of
Leptotrombidium often does not itch, or at least not as intensely, as those of Eutrombicula. Also,
a black necrotic lesion known as an eschar develops where the chigger fed.