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How to identify it
- The caterpillar is an inchworm up to about 35 millimeters (1.4 inches) long. Its color varies from gray to brown or burnt red-brown, or yellow to light brown, with wavy rusty brown to gray lines on the back and a broken yellow line down the middle.[1][2]
- Along each side runs a broad yellow (sometimes gray or yellow-green) stripe or a row of pale patches, broken by brown areas around each breathing hole. Well-marked caterpillars have pale diamond shapes on the back of the front abdominal segments.[2][1]
- The head is pale brown with a dark herringbone pattern on each side, and each abdominal segment has a pair of dark bumps near its rear edge.[2]
- Caripeta caterpillars are variable and hard to tell apart. The USDA Forest Service guide recommends rearing them to the moth stage when a positive identification is needed.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Brown pine looper (Caripeta angustiorata) and northern pine looper (Caripeta piniata) | These relatives are found more often on pine. A Caripeta inchworm on hemlock, spruce, fir or larch is very likely the gray spruce looper. The brown pine looper's pale patches on the back are less diamond-shaped, with the front half open and poorly defined.[1] |
Where it lives
It lives in coniferous forests across Canada and, in the eastern United States, south to Georgia in the mountains. Natural Resources Canada also lists western hosts such as Sitka spruce, shore pine, western hemlock and western redcedar.[1][2]
Biology and life cycle
Hosts include fir, spruce (including black, white, Norway and Sitka spruce), hemlock, larch, jack pine and other pines, northern white cedar, western redcedar and Douglas-fir.[1][2]
The pupa spends the winter. In Canada the moths fly in June and July, and each female lays up to 75 eggs on the host's needles. Caterpillars are present from July to mid-September and pupate in August.[2]
In Connecticut and Maryland there is one generation a year, with grown caterpillars from August to November; the species is moderately common there.[1]
Damage and signs
- The caterpillars feed alone and move about freely on the foliage, eating the needles. Natural Resources Canada describes it as common and occasionally destructive.[2]
Health risk
The sources describe it only as a conifer-feeding caterpillar; they mention no harm to people.[1][2]
Control
Prevention
Neither the USDA Forest Service guide nor Natural Resources Canada recommends any control for the gray spruce looper.[1][2]
Common questions
- What is the brown inchworm on my spruce in the fall?
- One candidate is the gray spruce looper, whose grown caterpillars are found from August to November in Connecticut and Maryland. Caripeta inchworms found on spruce, fir, hemlock or larch are very likely this species.[1]
- Is the gray spruce looper a serious pest?
- Only occasionally. Natural Resources Canada calls it a common and occasionally destructive defoliator that feeds alone rather than in groups.[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, “Gray spruce looper, Trees, insects and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/8496 (accessed 2026-11-09)
- iNaturalist, “Caripeta divisata taxon page (order and family).” www.inaturalist.org/taxa/205213 (accessed 2026-11-09)