Arachnid
Chigger
Trombicula
Biology
Chiggers, various species within the Trombicula (or related) genera, are the larval stage of mites in the family Trombiculidae. These are not insects but arachnids. The parasitic stage is the six-legged larva, which is microscopic, typically less than 0.3 mm, and bright red or orange. Adult chiggers are eight-legged, larger (up to 1 mm), red, and free-living predators of small arthropods and their eggs. The life cycle involves egg, prelarva, larva (parasitic), protonymph, deutonymph (predatory), tritonymph, and adult. Only the larval stage feeds on vertebrates, including humans. Larval development from egg to host-seeking typically occurs in late spring and summer.
Behaviour
Chigger larvae do not burrow into the skin; instead, they attach to a host and inject digestive enzymes that break down skin cells, which they then ingest. They typically feed for a few days, often at constricted areas where clothing is tight or the skin is thin, such as ankles, armpits, or waistbands. The intense itching associated with chigger bites is an allergic reaction to their saliva and the liquefied skin tissue. After engorgement, the larva detaches and drops to the ground to molt into the nymphal stage, which, along with adults, are beneficial predators of small soil invertebrates.
Habits
Chiggers thrive in dense vegetation, tall grasses, weeds, and wooded areas, particularly in damp or humid environments. They are most active in late spring, summer, and early fall when temperatures are between 25-300C and humidity is high. Conducive conditions for human exposure include walking or sitting in infested areas without protective clothing. They are encountered in fields, forests, and even overgrown gardens. While their bites are irritating, they are not typically vectors of human disease in North America, but scratching can lead to secondary bacterial infections.
Control methods
- 1Wear long sleeves and pants in infested areas.
- 2Apply permethrin to clothing and exposed skin repellents.
- 3Shower immediately after outdoor activities.
- 4Avoid walking through tall grass and dense weeds.
- 5Keep lawns mowed short and remove brush piles.
- 6Apply acaricides to heavily infested outdoor areas.
Tailored to Chigger
IPM Procedure Checklist
Inspection
- Survey interior and exterior for evidence and conducive conditions
- Document findings with photos and a site map
- Place monitors to confirm activity
Identification
- Confirm Chigger (Trombicula) — not a look-alike
- Note life stage and risk level: Moderate
- Capture clear photos and samples for the record
Action Thresholds
- Trigger action when monitor counts trend up
- Re-evaluate weekly during active season
- Document trigger criteria in the IPM plan
Prevention
- Exclude entry points and harborage
- Improve sanitation and moisture control
- Modify habitat around the structure
Control Methods
- Wear long sleeves and pants in infested areas.
- Apply permethrin to clothing and exposed skin repellents.
- Shower immediately after outdoor activities.
- Avoid walking through tall grass and dense weeds.
Monitoring & Evaluation
- Service monitors on schedule and trend captures
- Re-inspect for Chigger activity at follow-up
- Adjust tactics based on data; report findings to client