A chigger is the parasitic larval stage of a common mite in the genus Trombicula . Several species of chiggers exist in the United States, but Trombicula alfreddugesi is most commonly encountered. The adult stage is not parasitic and is often seen in lawns and moving across pavement. In Missouri, the adult stage spends its winter in the soil and the females will deposit eggs during the first warm days of spring. It is this stage that attacks humans and causes so much discomfort.
Chiggers crawl about on vegetation, waiting to attach to a host.
Rodents, birds, livestock, snakes, toads and other animals serve as natural hosts. Humans are an accidental host. There are two to three generations of chiggers produced each year in Missouri, so the threat of being attacked exists from May until the first killing frost. Two enlarged views of the chigger. A. Larval parasitic stage.