IPM Checklist
Bagworms on Evergreens
The short answer
Those cone- or spindle-shaped bags of silk and dead needles hanging on an evergreen are the protective cases of bagworm caterpillars, which drag their bag along as they feed and enlarge it as they grow.
This matters more on conifers than on shade trees: heavily infested arborvitae, juniper, cedar, and spruce can be defoliated and killed, while deciduous trees are attacked but usually not seriously harmed.
The single most reliable control is hand-picking the bags any time from fall through early spring and destroying them, because each female's bag holds hundreds of overwintering eggs, and this must be done before the eggs hatch in May or early June.
If populations are too high to hand-pick, Bacillus thuringiensis (Bt) works only on young larvae, so it must be applied while the caterpillars are small in late spring and by mid-July at the latest.
How to recognize bagworm damage
Bagworms build a spindle- or cone-shaped bag from silk covered with pieces of the host plant's own foliage, so on an evergreen the bag is camouflaged with green or brown needles and is easy to mistake for a cone.
Clemson describes the bags as ranging from about a quarter inch to over two inches long, enlarging as the caterpillar inside grows and feeds.
Damage shows up as missing needles, a thinning canopy, and brown or bare branches; because the injury is not conspicuous early in the season, the University of Maryland notes infestations often go undetected until August, after severe damage is done.
Why evergreens are at greater risk
The University of Maryland states that conifers, especially arborvitae, cedar, juniper, and pine, are the most frequently damaged hosts, and that heavily infested shrubs and trees, particularly conifers, may be killed.
Deciduous trees such as sycamore, maple, locust, boxelder, and linden are also attacked but are not seriously damaged, because a broadleaf tree can push out a new flush of leaves while an evergreen that loses its needles often cannot recover.
That difference is why a bagworm population you might tolerate on a shade tree deserves prompt action on an arborvitae or spruce hedge.
Hand-picking: the most effective control
Each mature female lays a very large number of eggs inside her bag and then dies, so every bag you remove over winter erases the next spring's brood; Clemson reports roughly 500 to 1,000 eggs per bag.
Pick the bags off during fall, winter, and early spring and destroy them, and be sure to finish before the new generation hatches in May or early June.
- 1Scout in the dormant season — Walk each evergreen from fall through early spring and look closely for the small silk-and-foliage bags, which are easiest to spot once you know their shape.
- 2Snip the silk band — Clip or pull off each bag; the tough silk strand that fastens it to the twig can girdle a small branch if left, so remove the whole bag.
- 3Destroy the bags — Drop the bags into soapy water or bag and discard them away from the plants rather than tossing them on the ground, since the eggs inside can still hatch.
When to use Bacillus thuringiensis (Bt)
If a hedge is too large or too heavily infested to hand-pick, Bacillus thuringiensis is the least-toxic spray option, but its timing window is narrow.
Clemson advises applying Bt when the eggs are hatching in late spring and the larvae are small, repeating every 7 to 14 days as needed; the University of Maryland is explicit that Bt must be applied by mid-July because it works well only on young bagworms.
⚠ By August the caterpillars are large and their bags are big, and Bt and other sprays no longer give good control. If you find full-grown bags late in the season, plan to hand-pick them over the coming winter rather than spraying.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Clemson HGIC — Integrated Pest Management for Evergreen Bagworms on Conifers — Verifies arborvitae, cedar, juniper, Leyland cypress, and pine as most susceptible hosts; cone-shaped bags of host foliage and silk ranging from a quarter inch to over two inches; damage as missing needles, thinning canopy, and brown branches; roughly 500 to 1,000 eggs laid within each bag; removing bags during fall, winter, or early spring before eggs hatch; and applying Bacillus thuringiensis when eggs are hatching in late spring while larvae are small, repeating every 7 to 14 days.
- University of Maryland Extension — Bagworms on Trees and Shrubs — Verifies conifers (especially arborvitae, cedar, juniper, and pine) are most frequently damaged and heavily infested conifers may be killed, while deciduous trees (sycamore, maple, locust, boxelder, linden) are attacked but not seriously damaged; that bags are made of silk with attached leaf pieces; that homeowners should pick off bags in fall, winter, and spring and destroy them before the new generation hatches in May or early June; that Bt must be applied by mid-July because it works well only on young bagworms; and that injury is often undetected until August.