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How to identify it
- The moth is moderately large and mottled black and gray, with a network of black lines over black-gray scaling on the forewings, darker toward the base, and rounded, translucent hindwings with blackish hairs at the base. Males span 40 to 50 mm and females 50 to 64 mm.[1]
- The sexes look more alike than in other cossid moths; the female has threadlike antennae and a slightly stouter body, the male feathery antennae.[1]
- The grown caterpillar is 32 to 45 mm long, creamy white with a dark brown head and strong black jaws, a thoracic shield that ranges from pale yellowish to blackish brown, dark brown spiracles and a yellowish shield at the rear.[1]
- Signs on the tree are small entry holes in the bark, often in and around old wounds, from which frass or debris is pushed out and sap may bleed. A heavily attacked tree has piles of frass at its base, and split wood is riddled with tunnels.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Carpenterworm | The carpenterworm (Prionoxystus robiniae) is the widespread cossid of many hardwoods across the United States and southern Canada. Natural Resources Canada says the poplar carpenterworm adult looks similar, with mottled gray wings and body.[1][2] |
| Aspen carpenterworm | The aspen carpenterworm (Acossus populi) is a sister species found in poplars and cottonwoods from coast to coast.[2] |
Where it lives
A northern species: in the United States from New Jersey west to Illinois and North Dakota, and in Canada from Quebec and Ontario west to British Columbia.[1][2]
Biology and life cycle
The hosts are poplars, including trembling aspen and balsam poplar.[1][2]
The caterpillar bores in the wood of the living tree and pupates inside it. The pupa is narrow, shiny, wrinkled, brownish black and about 30 mm long.[1]
Moths emerge in June and July. How long the life cycle takes is not known.[1]
Birds, especially woodpeckers, may take up to 75 percent of a wood-borer population and are probably the most effective natural control. Parasitic wasps also attack wood borers, and in the United States fast-growing decay fungi have been found trapping pupae in their tunnels.[1]
Damage and signs
- Wood borers in living hardwoods often go unnoticed until severe damage has been done. Tunneled trees are weakened structurally and prone to wind and snow breakage, especially when attacked repeatedly, and the stress leaves them more open to drought and disease.[1]
Health risk
The sources describe it only as a wood borer of poplars and report no effect on people.[1][2]
Control
Prevention
Most wood borers lay eggs at wounds and scars, so avoid injuring ornamental poplars with careless cultivation, pruning or mowing. Healthy, well-growing trees resist attack best; water them during drought.[1]
Biological control
Woodpeckers and parasitic wasps are the main natural checks on wood borers, so leaving birds to work the trunk helps.[1]
Common questions
- What is pushing sawdust-like frass out of holes in my aspen trunk?
- Frass extruded from small bark holes, often around old wounds and sometimes with bleeding sap, is the sign of a wood borer. In the northern states and Canada the poplar carpenterworm is one of the moths whose caterpillars tunnel living poplar and aspen wood.[1]
- How do I protect poplars from carpenterworms?
- Avoid wounding the bark, keep the trees vigorous and water them in drought. Wood borers prefer wounds and scars for egg laying and stressed trees for feeding.[1]
Sources
- Natural Resources Canada, Canadian Forest Service, “Poplar carpenterworm, Trees, insects and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/8245 (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)
- iNaturalist, “Acossus centerensis taxon page (order and family).” www.inaturalist.org/taxa/212364 (accessed 2026-11-10)