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How to identify it
- The nest is the giveaway: a loosely webbed, globular mass of coarse brown frass pellets and silk, roughly 2 to 6 inches long, wrapped around needles on a twig, with the caterpillars living in silk tubes that run through it. A nest may hold a couple of caterpillars or as many as 78.[1][2]
- Full-grown caterpillars are about 0.6 inch (18 to 20 mm) long and yellowish brown with dark brown lengthwise stripes, two on each side; some are so dark that the stripes merge. The head is yellowish brown marked with dark brown.[1][2][3]
- The adult moth has a wingspread of about 25 mm with a purple-black base, a grayish middle and a blackish outer part to the forewing. Adults are attracted to lights.[2][1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Pine tube moth | Its larva draws 5 to 20 needles together with silk into a tube and eats their tips, mostly on white pine; there is no frass-packed nest, and the pine webworm prefers hard pines such as jack and pitch pine.[2] |
| Pine needleminer | Tiny pine caterpillars that stay inside the needles and turn them brown without building any nest; the young pine webworm also mines needles briefly before it starts webbing.[1][3] |
Where it lives
Southern Canada and most of the eastern half of the United States. The Forest Service lists jack pine as the preferred host in the Lake States and pitch pine in the Northeast; UMass adds loblolly, longleaf, mugo, red, Scotch, shortleaf, Virginia and white pines, with slash pine a host in the Southeast.[2][1]
Biology and life cycle
The insect spends the winter in a silk cocoon in the soil and pupates there. The UMass guide describes the overwintering stage as a larva that pupates in spring; the Forest Service's 2004 conifer caterpillar guide says the pupa overwinters. Moths appear from June into July and possibly early August.[1][3][2]
Females lay their tiny eggs in single rows along pine needles, up to 20 eggs on one needle. The young caterpillars spin loose webbing around a cluster of needles and then mine inside a needle; once too large to mine, they feed on needles from silk tubes inside the growing nest of frass and silk.[1][2]
Nests are present from late June through July in the northern part of the range, and the caterpillars keep feeding inside them into the fall; mature caterpillars are found from August to October and drop or crawl to the soil by late September to spin their cocoons.[1][3]
There is one generation a year in the north. UMass reports two generations from Virginia to Florida and even three in some Florida locations; the Forest Service says there may be two in the South.[1][2]
Damage and signs
- Young seedlings up to 2 feet tall are sometimes completely defoliated and killed by the larvae in a single nest, which is why the pine webworm is often troublesome in pine plantations.[2]
- On Christmas trees and landscape pines the ugly nests of dead needles, silk and frass on the terminal twigs are the main problem; growers may be unable to sell infested trees. The damage is usually noticed only after the caterpillars have finished feeding and left.[2][1]
- In southern New England most nests on pitch pine are found near ground level.[3][1]
Health risk
None of the sources mentions any effect on people; this is a plant pest, and its caterpillars are not described as stinging.[1][2]
Control
Prevention
Look for nests on the shoots from late June onward, especially low on pitch pines, and check Christmas tree and seedling blocks, where the insect does the most harm.[1][2]
Traps and physical control
Hand-pick or prune out the webbed nests while caterpillars are still inside and destroy them. Removing empty nests after the caterpillars have gone to the soil will not reduce next year's population, although it tidies up the tree.[1]
Biological control
Parasitic wasps and flies attack the caterpillars, including the ichneumonid Syzeuctus elegans and tachinid flies in the genus Eufrontina, and chickadees and nuthatches tear nests apart to eat the larvae.[1]
Pesticides
UMass lists acephate, azadirachtin, Bacillus thuringiensis kurstaki, bifenthrin, carbaryl, cyfluthrin, deltamethrin, indoxacarb, malathion, permethrin and pyrethrins, plus horticultural oil against the eggs, as active ingredients labeled for this pest in Massachusetts; make applications after bloom to protect pollinators.[1]
Common questions
- What is the ball of brown pellets and webbing on my pine?
- Almost certainly a pine webworm nest: a loose mass of frass pellets and silk, a few inches long, with one or more striped caterpillars living in silk tubes inside it and feeding on the enclosed needles.[1][2]
- Will pine webworms kill my tree?
- A single nest can kill a seedling under 2 feet tall, but on larger landscape pines the harm is mostly the unsightly nest and the brown needles inside it.[2][1]
- How many generations are there?
- One a year in the north; UMass reports two from Virginia to Florida and up to three in parts of Florida.[1]
Sources
- UMass Extension Landscape, Nursery and Urban Forestry Program, University of Massachusetts Amherst, “Pococera (formerly Tetralopha) robustella, Pine Webworm, Insect & Mite Guide (Professional Guide for IPM in Trees and Shrubs).” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/pococera-formerly-tetralopha-robustella (accessed 2026-11-10)
- USDA Forest Service, “Eastern Forest Insects, Miscellaneous Publication 1175 (W. L. Baker, 1972; scanned copy).” archive.org/details/easternforestins1175bake (accessed 2026-11-10)
- USDA Forest Service, Forest Health Technology Enterprise Team, “Pine Webworm (Pococera robustella), from Caterpillars on the Foliage of Conifers in the Northeastern United States, FHTET-2004-01 (C. T. Maier, C. R. Lemmon, J. M. Fengler, D. F. Schweitzer and R. C. Reardon, 2004), Bugwood wiki archive.” wiki.bugwood.org/Archive:Caterpillars/Pococera_robustella (accessed 2026-11-10)
- iNaturalist, “Pococera robustella taxon page (order and family).” www.inaturalist.org/taxa/361321 (accessed 2026-11-10)