CHIGGER

also called scrub mite, harvest mite, bte rouge, or chigger mite the larva of any of the 10,000 species of the invertebrate suborder Prostigmata of the subclass Acarina (sometimes Acari, or Acarida). The name is also erroneously applied to an insect better known as the chigoe, jigger, or jigger flea. Chiggers range in length from 0.1 to 16 mm (0.004 to 0.6 inch). The body armour is thin and discontinuous. Certain species have eyes, others have none. Spiracles, or breathing pores, when present, are at the base of the first pair of appendages or elsewhere on the front part of the body. Some species are terrestrial in habit, others live in fresh or marine water. Some are predacious, others are scavengers, parasites, or plant feeders. Various chiggers are pests of man, either as parasites or as carriers of disease. Attacks of chiggers often result in a dermatitis accompanied by intense itching. In North America the common chigger that attacks humans is Eutrombicula alfreddugsi (also called Trombicula irritans). This species occurs from the Atlantic coast to the Midwest and southward to Mexico. The tiny larvae easily penetrate clothing. Once on the skin surface, they attach themselves and inject a fluid that digests tissue and causes severe itching. The surrounding tissue hardens, forming a tube. After feeding, the larva drops to the ground and sheds its skin, first becoming a nymph, then an adult. These stages are not parasitic on vertebrates but feed on plant materials and perhaps on other arthropods. The eggs are laid by the adult singly on the ground or on the leaves or stems of low-growing plants. Other species of chiggers that were formerly considered to be members of Trombicula but usually are now classified as separate genera include Eutrombicula splendens and E. batatus of North America. In Europe Neotrombicula autumnalis attacks not only humans but also cattle, dogs, horses, and cats. In the Orient certain species of Leptotrombidium carry the disease known as scrub typhus.