Hairy caterpillar
Swarming hairy defoliators — dense groups when young, marching armies when older, stripping the crop leaf by leaf.
- Pest type
- Defoliating caterpillar
- Attacks
- Leaves (many kharif crops)
- Worst in
- Monsoon onset (kharif)
- Main risk
- Swarming defoliation
Overview
Hairy caterpillars (including the Bihar hairy caterpillar and red hairy caterpillar) are conspicuous, hairy larvae of moths that appear with the monsoon and defoliate groundnut, pulses, soybean, sesame and other kharif crops. The moths lay eggs in masses, so the young caterpillars hatch together and feed as a dense group, skeletonising a few leaves near where they hatched.
As they grow they disperse and, in the older stages, move across the field in large numbers — the "marching" habit — eating foliage as they go and, in a bad year, stripping whole crops. The dense grouping of the young larvae is the pest’s weakness: destroying the leaves carrying the clustered young stage removes huge numbers at once, long before they scatter and march.
How to identify it
- Conspicuous caterpillars densely covered in long hairs, in colours from yellow-brown to reddish or dark, depending on species.
- Young larvae clustered together on a few skeletonised leaves near the egg mass — the group stage.
- Older larvae dispersed across the field, or moving in numbers ("marching") between fields.
- Appearance timed with the monsoon and the first crop growth.
The damage it does
- Rapid defoliation, from skeletonised patches by the young group to whole-plant stripping by the marching older larvae.
- Severe loss in a heavy outbreak year, sometimes defoliating young groundnut and pulse crops.
- Fast movement between fields, so an untreated outbreak spreads quickly across an area.
- Loss concentrated at crop establishment when defoliation hurts most.
When to act
- Act at the grouped young-larva stage — this is by far the easiest and most effective time, before they scatter and march.
- Scout the crop from monsoon onset and after the moth flights (light-trap catches signal them).
- Once the larvae are large and marching, control is harder, so early detection is key.
Organic & cultural control
- Collect and destroy the leaves carrying the clustered young larvae — removing the group stage takes out huge numbers at once.
- Use light traps to catch the adult moths at monsoon onset and reduce egg-laying, and dig a trench/barrier to stop marching larvae entering a clean field.
- Spray Bt or SlNPV-type biologicals and neem against young larvae, and encourage birds with perches.
- Deep-plough after harvest to expose pupae and follow crop rotation.
Chemical control
- Target the young larvae with a CIB&RC-registered insecticide for the crop, while they are still grouped and exposed.
- For large marching larvae, an evening application or a poison bait is more effective, and a barrier trench with insecticide dusting stops them entering fresh fields.
- Rotate insecticide groups and observe the pre-harvest interval.
- Confirm the current recommendation and dose for your crop and zone with your local KVK.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
Swarms of hairy caterpillars are eating my groundnut/pulse crop. How do I stop them?
Act while they are young and still clustered together on a few leaves — collect and destroy those leaves to remove huge numbers at once, and spray Bt/neem on the young larvae. This is far easier than fighting the older larvae once they scatter and march across the field. Light traps at monsoon onset reduce the moths that start it.
Why is the young stage the best time to control hairy caterpillar?
Because the young larvae hatch from an egg mass and feed as a dense group on just a few leaves, so destroying those leaves takes out large numbers in one step. Once they grow, they disperse and even march between fields, becoming much harder to control. Early detection and group destruction is the key.
The caterpillars are marching into my field from next door. What can I do?
Dig a trench or make a barrier along the field edge (and dust it with a registered insecticide) to stop the marching larvae crossing in, and treat them at the barrier. For larvae already in the crop, an evening insecticide application or poison bait works better than a daytime spray. Coordinate with neighbours, since the outbreak is area-wide.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.