Field Identification
The larva of a moth that lives inside a spindle-shaped silk bag camouflaged with host plant bits—often mistaken for a pine cone until branches go bare. Caterpillars crawl while wearing the bag, feeding on needles and leaves of many conifers and some broadleaf ornamentals. Heavy infestations cause branch dieback and can kill stressed trees. Common from temperate eastern North America through much of the U.S. and into suitable climates in Mexico and Central America wherever hosts occur; evergreen plantings in zones roughly 5–9 are most often affected, with localized pressure in warmer pockets.
Male moths are dark and winged; females are wingless and remain in the bag. Bags grow from pencil-tip size to about 2 inches (50 mm) by late summer, hanging from twigs on a silk strand. Larvae are dark with lighter markings and withdraw fully into the bag when disturbed. Winter eggs are inside the female’s old bag—look for persistent bags after leaf drop on deciduous hosts.
How to Deal With It
Organic Control Methods
Bacillus thuringiensis kurstaki (Bt k) targets young larvae when they are actively feeding and exposed; thorough spray into canopy is required. Neem or spinosad can follow label directions for caterpillars on ornamentals. Horticultural oil applied during dormant windows can help reduce overwintering eggs inside bags where timing matches label allowances for the host species.
Ichneumonid and braconid parasitoids attack bagworm larvae inside cases; birds and vespid wasps rip open bags. Diverse understory and reduced broad-spectrum spraying helps these enemies persist in shelterbelts and yard edges.
Avoid shearing conifers into “meatballs,” which creates dense interiors perfect for hidden bags; open structures improve spray penetration and bird access. Replace chronically infested specimen trees when bags number in the dozens and recovery is unlikely. Do not move nursery stock with bags attached onto uninfected sites.
From late fall through spring before hatch, pick and destroy bags—burn where allowed, hot-soapy soak, or seal in bags for landfill. For reachable trees, this alone can break a local outbreak. Clip heavily infested twigs when removal improves access and aesthetics.
Inspect evergreens twice a year—early summer for tiny new bags and fall for missed ones. Isolate new ornamental conifers until checked. In windbreaks, stagger species and ages so a single bagworm year does not thin an entire screen at once.
Let Nature Handle It
Natural Enemies
- Ichneumonid Wasps
- Braconid Wasps
- Vespid Wasps (Vespidae)
- Insectivorous Birds
Threat Map