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How to identify it
- The caterpillar is a variable mottle of green, yellow, tan, white, brown and black, or light reddish brown. Many show a row of arrowhead, chevron or diamond marks down the back.[1][2]
- The dark mottling is usually heaviest around the breathing holes (spiracles), which are white or pale brown ringed in black. The eighth abdominal segment is slightly humped and often has a small white spot.[1]
- The head is light brown and heavily mottled. Full-grown caterpillars reach about 27 mm in Natural Resources Canada's measurements and up to 3.5 cm (about 1.4 inches) in the USDA Forest Service guide.[1][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Esther variant (Hypagyrtis esther) | Hypagyrtis is a hard genus to sort out. The USDA Forest Service authors treat the pine measuringworm as a northern species and the Esther variant as its replacement in pine barrens and coastal plain areas, south to Georgia and Texas, where it seems to prefer pines.[1] |
| One-spotted variant (Hypagyrtis unipunctata) | Possibly the most widely encountered inchworm in the East. It comes in green, gray, brick red or brown, lacks prominent bumps, and usually has a diffuse pale patch on the fifth abdominal segment.[1] |
Where it lives
It lives in coniferous woodlands and forests from coast to coast in Canada, from British Columbia east to Newfoundland. In the eastern United States it reaches south to Maryland, the Great Lakes region and the mountains of Georgia.[1][2]
Biology and life cycle
Hosts include fir, hemlock, larch, pine and spruce. Natural Resources Canada names Douglas-fir, western hemlock, Engelmann spruce and white spruce as the main hosts in British Columbia, with others such as lodgepole pine, ponderosa pine, western larch and western redcedar.[1][2]
The caterpillar is the overwintering stage, and it spends the winter exposed on bark or foliage.[1][2]
In Canada the caterpillars resume feeding in spring and continue until June or July. They pupate in July and August, the moths emerge and lay eggs in the same months, and the eggs hatch soon after; the new caterpillars feed until early fall.[2]
Farther south, in Connecticut and Maryland, there are two generations, with full-grown caterpillars in May and June and again in July and August; the species is locally common there.[1]
Damage and signs
- The caterpillars feed alone, moving freely over the foliage and eating needles. Natural Resources Canada calls it a common but innocuous defoliator.[2]
Health risk
The USDA Forest Service and Natural Resources Canada accounts cover only its looks, hosts and seasons; neither reports any risk to people.[1][2]
Control
Prevention
Because it feeds alone and is regarded as innocuous, neither source suggests treating trees for this inchworm.[1][2]
Common questions
- Does the pine measuringworm only eat pine?
- No. It feeds on fir, hemlock, larch, spruce and Douglas-fir as well as pine, and in British Columbia its main hosts are Douglas-fir, western hemlock and spruces.[1][2]
- Why do I see inchworms on my conifers in early spring?
- One possibility is the pine measuringworm. Its caterpillars spend the winter out in the open on bark or needles and start feeding again in spring.[1][2]
Sources
- USDA Forest Service, Forest Health Technology Enterprise Team, “Geometroid Caterpillars of Northeastern and Appalachian Forests, FHTET-2001-10 (D. L. Wagner, D. C. Ferguson, T. L. McCabe and R. C. Reardon, September 2001; scanned copy).” archive.org/details/geometroidcaterp00wagn (accessed 2026-11-09)
- Natural Resources Canada, Canadian Forest Service, “Pine measuringworm moth, Trees, insects and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/8808 (accessed 2026-11-09)
- iNaturalist, “Hypagyrtis piniata taxon page (order and family).” www.inaturalist.org/taxa/143128 (accessed 2026-11-09)