chigger, minute, six-legged, reddish larva of the harvest mite, one of various red bugs widely distributed throughout the world and common in the S United States. Attaching itself by its mouthparts to the skin of its vertebrate host, the chigger injects saliva that destroys cells and may cause an intense irritation known as red-bug dermatitis. The food of the chigger consists of the cellular contents and tissue fluid of the host. Certain Asian species carry minute organisms (rickettsias) that cause scrub typhus, a disease of humans. Chiggers are classified in the phylum Arthropoda, class Arachnida, order Acarina, family Trombidiidae.