Several kinds of mites may infest a person for several days or somewhat longer. Most prominent are the ticks, some of which may attach and blood feed for just minutes, others for days or a week or more. We offer a separate resource on ticks and encourage you to visit those pages. Another group of mites that infest for a day or more is composed of the mites known as chiggers.
Trombiculids (e.g. Trombicula [=Eutrombicula] alfreddugesi in the U.S.) are nearly microscopic mites that feed on different sources depending upon the mite’s stage of development. In their larval stage (a stage soon after hatching from the egg), chiggers attach to and feed upon skin fluids and cells of animals, but not on their blood. Depending on the kind of chigger, they may attach to reptiles, amphibians, birds and mammals. They occasionally – and accidentally – attempt to feed on people, but these tend not to do so successfully.
Chiggers neither bite nor burrow into skin, but instead insert their chelicerae (a kind of mouthpart) into skin and then salivate. The saliva breaks down skin cells and causes formation of a hard tube – called a stylostome – at the feeding site. After a day or so, reactions to the saliva and the stylostome cause local and often intense irritation, often manifesting as a raised and itchy papule. The irritation and itching frequently causes a person to scratch the site, and this action effectively scrapes off the larval mite if it hadn’t already finished feeding and detached by itself. The remaining stylostome will continue to cause irritation for days or more, thereafter. For this reason, the chiggers, themselves, are generally not observed on the skin, but the lesions are certainly noticed.
Chiggers in North America are not known to transmit infections, but those in parts of the Asia Pacific region transmit a pathogen that causes a serious disease of humans called scrub typhus. As with the itching that may result from virtually any kind of arthropod bite, scratching may cause secondary infection from bacteria on the skin or under the fingernails.
If the larval chigger survives, it will drop off and mature through a series of nymphal stages and later to the adult. Nymphs and adults are non-parasitic; instead, they feed on other tiny arthropods, their eggs and even plant tissues.
As with ticks, chigger larvae accumulate on the ground and may climb onto low vegetation where they more likely encounter an animal. People acquire chiggers when they wander through grasslands or other habitats where and when these mites are abundant and active. Insect repellents can lessen the chances of chigger attachment to a person.