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How to identify it
- Look for loose silk webs or tubes at the base of the needles, filled with frass, clipped needles and cast skins; they get more conspicuous as the season goes on.[1][2][3]
- Larvae are olive green to greenish brown with purplish-red stripes along the body and an orange-yellow to light brown head, and are about 15 to 20 mm (roughly 5/8 to 3/4 inch) long when full grown.[2][1]
- Unlike moth caterpillars, the larvae have no fleshy prolegs on the abdomen, only short legs behind the head, so they crawl poorly and quickly pull back inside the silk when disturbed.[1][2]
- Adults are sawflies: females are black or bluish black with a red head, and males are black with a yellow face and yellow front legs.[2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Jack pine budworm | Also webs pine needles together, but its caterpillars feed on the new growth from mid-May to early July and turn reddish brown with cream spots as they grow.[3] |
Where it lives
Introduced from Europe and first recorded in North America in Pennsylvania in 1925, it has spread through much of the northeastern United States and the Lake States, and it has been in Ontario since 1961.[1][2]
Biology and life cycle
There is one generation a year: larvae overwinter in earthen cells a few inches down in the soil under the host and pupate in spring; UMass puts adult emergence at about mid-April to mid-May, and in Ontario it runs mid to late May.[1][2]
Females cut small slits in the previous year's needles and lay their eggs end to end in small groups; the eggs hatch in about two weeks.[1][2]
Young larvae spin webs at the base of the needles, cut needles off and pull them into the web to eat; older larvae may move off to feed alone from their own silk tubes, and after about 18 to 28 days of feeding they drop to the soil.[1][2]
Some larvae stay in the soil through two winters before they emerge as adults.[2]
Damage and signs
- Larvae strip the older needles first; new growth is usually spared but can still die from the stress on a heavily defoliated tree.[1][2]
- Hosts include red and eastern white pine, which females prefer for egg laying, plus Scots, Austrian, mugo, Japanese red and jack pine.[1][2][3]
- Repeated heavy defoliation can kill pines: UMass notes that more than 70 percent defoliation in consecutive years may lead to tree death, and weakened pines can then be attacked by bark beetles or fungal disease.[1]
- For decades it was mainly a pest of young pines in Christmas tree farms, nurseries and landscapes; since the early 1990s it has also defoliated older red and white pine plantations in Ontario and New York.[2]
Health risk
It feeds only on pines; neither source reports any harm to people or pets.[1][2]
Control
Prevention
Watch for the distinctive adults in May, often seen flying in the tops of host trees, to judge whether treatment is needed and when.[2]
Traps and physical control
On landscape pines, small infestations can be pruned out and the webbed branches destroyed.[1]
Biological control
Natural enemies usually keep it in check in Europe; a European tachinid fly has been released in Ontario, and Natural Resources Canada names the tachinid Myxexoristops hertingi as the most promising biological control agent.[1][2]
Pesticides
Sprays work poorly once the webs are large and dense because the larvae feed inside; if treatment is needed, apply it just before or within a day or two after egg hatch, or spray forcefully enough to penetrate the webs, and follow the label.[1][2]
Common questions
- What are the silk tubes full of needles on my pine?
- Webs or tubes packed with clipped needles and frass at the base of older needles in late spring point to pine false webworm larvae feeding inside.[1][2][3]
- Is the pine false webworm a moth?
- No; despite the name it is a sawfly, a relative of bees and wasps named for the saw-like egg-laying organ the female uses to slit needles.[2]
- Will pine false webworm kill my pine?
- Light infestations are mostly unsightly, but heavy defoliation several years in a row can kill pines, especially young or stressed trees.[1][2]
Sources
- UMass Extension Landscape, Nursery and Urban Forestry Program (Landscape Insect & Mite Guide), “Acantholyda erythrocephala (Pine False Webworm).” www.umass.edu/agriculture-food-environment/landscape/publications-resources/insect-mite-guide/acantholyda-erythrocephala (accessed 2026-10-17)
- Natural Resources Canada, Canadian Forest Service (Trees, insects and diseases of Canada's forests), “Pine false webworm (J. P. Brandt, revision 2024).” tidcf.nrcan.gc.ca/en/insects/factsheet/1000130 (accessed 2026-10-17)
- University of Minnesota Extension (What's wrong with my plant?), “Pine: clumps of webbed needles.” apps.extension.umn.edu/garden/diagnose/plant/evergreen/pine/needlesclumps.html (accessed 2026-10-17)
- iNaturalist, “Acantholyda erythrocephala taxon page (order and family).” www.inaturalist.org/taxa/212218 (accessed 2026-10-06)