Common Name: Chiggers
Scientific name: Trombicula (Eutrombicula) alfreddugesi (Oudemans) and T. splendens Ewing
Family: Trombiculidae (harvest mites)
Description: Chigger mites are also called “jiggers” and “redbugs.” The parasitic larval stages are very small, requiring a hand lens or microscope to see. The larval stage is less than 1/150 inch long, having a hairy yellow, orange to light red body and six legs. The nymphal stage resembles the adult, having eight legs, and brilliant red 1/20 inch long figure-eight shaped bodies.
There are many chiggers species in Texas, but only a few are annoying to humans. Other species live in moist habitats, swamps, bogs, rotten logs and stumps.
Life cycle: Adult chiggers spend the winter in protected sites such as cracks in the soil and leaf litter on the ground. In the spring, they lay eggs that hatch into the parasitic larval or “chigger” stage. This is the stage that attaches to humans or animals. After feeding for several days, the larva dislodges, drops to the ground and changes into a non-feeding pupa-like second larval stage (the nymphochrysalis) where it develops into a free-living nymphal stage. After passing through two nymphal stages (one feeding, one non-feeding), the mite becomes an adult. Development can be completed in 40 to 70 days, with up to four generations being produced per year.
Habitat and Food Source(s): In addition to humans, the parasitic larval stage of chiggers feed on domestic and wild animals, including birds, reptiles and some amphibians. Chiggers populations develop in fields and weedy areas, particularly in areas with tall grasses and wild berry patches. Although active from spring through fall, they are more of a problem in early summer, when lush vegetation is prevalent. The larval stages congregate on the tips of plants and other objects from where they crawl onto hosts detected by movement, carbon dioxide, odor and other stimuli. The free-living nymphal and adult stages are predaceous, feeding on insect eggs, small insects and other organisms like Collembola and their eggs in ground litter where they occur.
Pest status: Plant feeder, causing stippling or bronzing of leaves. On humans, the parasitic larval stage attaches to tender skin with their mouthparts to feed for several days, much like ticks. They prefer to attach in areas where clothing fits tightly such as underneath belt lines and sock bands, and where skin is wrinkled such as behind the knees. The larva injects a digestive fluid that disintegrates the skin cells and forms a feeding tube (stylastome) into the skin. The skin swells around the chigger, making the chigger appear to be burrowing into the skin. The itching, caused by the injection of digestive enzymes, may persist for several days after the chigger dislodges.
Literature: Hamman 1983. Reviewed Burke 3/1996; Olson 11/96.