Chigger

Chiggers are not a distinct species but the larval stage of trombiculid mites, a large family of arachnids found on every continent except Antarctica. The name is applied loosely to dozens of species in the genus Trombicula and its relatives, all of which share the same unusual life history: only the six-legged larva is parasitic, while the nymph and adult stages that follow are free-living predators unrelated in habit to the larva.

Because the larvae are so small, a chigger encounter is usually recognized only by the aftermath rather than by seeing the animal itself. They are most active in warm, humid months and are common in overgrown lawns, pastures, and berry patches, giving rise to old regional nicknames like "berry bugs" or "harvest mites."

• Larva is oval, six-legged (unlike the eight-legged nymph and adult), and pale yellow to orange-red
• So small it typically requires a hand lens or microscope to see individuals clearly
• Often found in loose clusters on the tips of grass blades or leaf litter, waiting to contact a host
• Free-living adults are larger (still under 1 mm), bright red, and covered in fine velvety hairs, resembling miniature red velvet mites
• Easily confused with tiny spider mites, but chigger larvae are found on vegetation tips in open habitat rather than on the underside of garden leaves

Trombiculid mites occur worldwide in temperate and tropical regions, with the greatest activity in warm, humid climates. Larvae are most abundant in tall grass, weedy fields, forest edges, and shaded, moist vegetation from late spring through early fall in temperate zones, and year-round in warmer climates. Adults and nymphs live in the same general habitats but stay within leaf litter and topsoil rather than climbing vegetation.

Larval chiggers practice a behavior called questing: they climb to the tip of a grass blade or other low vegetation and wait with legs outstretched until a potential host brushes past. After a single brief feeding episode on skin cells, the larva drops off and molts into a nymph, never feeding on a host again. Nymphs and adults are free-living generalist predators and scavengers, feeding on small invertebrate eggs, springtails, and decaying organic matter in the soil, making them part of the decomposer food web rather than parasites.

Females lay eggs in soil or leaf litter, which hatch into six-legged larvae, the only parasitic stage. After feeding once, the larva drops to the ground and molts into an eight-legged, non-feeding nymphochrysalis, then an active nymph, and finally an adult, both of which are free-living predators. Depending on climate, trombiculid mites may complete one to several generations per year, typically overwintering as nymphs or adults in protected soil and litter.