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How to identify it
- The caterpillar is light green with a creamy yellow stripe low along each side, a thinner yellow stripe higher on each side of the back and a thin dark green line down the middle of the back. The head is plain yellow-green.[2][1]
- Full grown it is about 24 millimeters (1 inch) long, and its hind legs are conspicuously enlarged.[2][1]
- Its resting posture is unusual among conifer-feeding inchworms: it rolls its head under its thorax, sometimes tucked right under the third pair of legs, so the front of the body looks like a fist.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Powder moth caterpillars (Eufidonia) | They look similar, but in the yellowlined forest looper the low side stripe stops at the first breathing hole behind the head, while in powder moth caterpillars it runs at least to the head.[1] |
| Cladara anguilineata | A close relative that occurs alongside it over much of the East, from Maine to the Gulf Coast states. The USDA Forest Service guide notes that its own photo of the yellowlined forest looper may actually show this species.[1] |
Where it lives
It occurs across Canada and south in the United States to Georgia (in the mountains) and Missouri, in forests and woodlands. Natural Resources Canada's host list includes western conifers such as Sitka spruce, western hemlock and western redcedar.[1][2]
Biology and life cycle
The caterpillars feed on conifers: fir, spruce, hemlock, larch and pine, plus Douglas-fir and western redcedar in Canada.[1][2]
The pupa spends the winter. In Canada the moths come out in May, caterpillars are present from May to July, and they pupate in July and August.[2][1]
In Connecticut there is one generation, with grown caterpillars in June, and the species is very common there.[1]
Damage and signs
- The caterpillars feed alone and move about freely on the needles. Natural Resources Canada describes the species as a common, innocuous defoliator.[2]
Health risk
The sources describe it only as a conifer-feeding caterpillar; they mention no harm to people.[1][2]
Control
Prevention
No control is suggested by either source; Natural Resources Canada calls this looper innocuous.[2][1]
Common questions
- What is the green inchworm curled up like a fist on my spruce?
- A green inchworm with yellowish side stripes that rests with its head rolled under its body, on fir, spruce, hemlock or another conifer in late spring, fits the yellowlined forest looper.[1][2]
- Will yellowlined forest loopers hurt my conifers?
- Natural Resources Canada describes this species as a common, innocuous solitary defoliator.[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, “Yellowlined forest looper, Trees, insects and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/8520 (accessed 2026-11-09)
- iNaturalist, “Cladara limitaria taxon page (order and family).” www.inaturalist.org/taxa/217054 (accessed 2026-11-09)