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How to identify it
- Most caterpillars are pale green with a broad white stripe along each side of the back and a cream to creamy yellow stripe lower down near the breathing holes. A dark green stripe edged in white runs down the middle of the back.[1][2][3]
- In the last stage a second, brown form is common: brown, maroon or purplish brown, mottled with black and white, with a dark mark on the back of each abdominal segment. Both forms are green until that final stage; the green one blends in on the needles and the brown one on twigs.[1][2][3]
- It is small, under 2 cm (about 3/4 inch) when full grown. In the experience of the USDA Forest Service conifer guide's authors, it is the most common and smallest Macaria inchworm on eastern larch.[1][2][3]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Owen's larch looper (Macaria oweni) | Shares larch with this species from northern New England into Canada. Owen's larch looper often has a well-defined dark stripe beneath the white stripe on the back, which is absent or weak in the green larch looper.[1] |
| Spruce-fir looper (Macaria signaria) | Occasionally feeds on larch. Its caterpillar is more blue-green, with proportionately thinner stripes.[1] |
Where it lives
It occurs from western Canada and the Yukon east to Newfoundland and Labrador and Nova Scotia. In the United States it reaches south to Oregon in the West and to Massachusetts, Connecticut, Maryland and the Great Lakes region in the East, but it is rare as far south as Pennsylvania and Maryland.[1][3]
Biology and life cycle
Larch is the main host: tamarack (eastern larch) and western larch. Natural Resources Canada also lists secondary hosts such as spruces, firs, hemlocks, pines, Douglas-fir and juniper.[1][2][3]
The pupa overwinters in the soil, in debris or in sphagnum moss. In Canada the moths emerge in June and lay their eggs one at a time on the needles; the eggs hatch in about 14 days, and caterpillars feed from June to August before pupating.[2][3]
There are one or two generations a year, with a second generation more likely in the southern part of its range. In Connecticut and Maryland there are two, with full-grown caterpillars from June to November.[1][2]
By day the caterpillars rest among the needle clusters. At night they may hang from larch needles, which the USDA authors liken to little Christmas tree ornaments.[1]
Damage and signs
Health risk
It is a needle-feeding inchworm; the Forest Service and Natural Resources Canada describe no danger to people from it.[1][3]
Control
Prevention
The sources describe its life history but offer no control measures for it on larch.[1][2][3]
Common questions
- What are the small green striped inchworms on my tamarack?
- A likely candidate is the green larch looper, the most common and smallest Macaria inchworm on eastern larch. It is pale green with white and cream stripes, though some grown caterpillars are brown.[2][1]
- Can it hurt a larch?
- It is frequently abundant and occasionally destructive, according to Natural Resources Canada.[3]
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)
- USDA Forest Service, Forest Health Technology Enterprise Team, “Green larch looper (Macaria sexmaculata), from Caterpillars on the Foliage of Conifers in the Northeastern United States, FHTET-2004-01 (C. T. Maier, C. R. Lemmon, J. M. Fengler, D. F. Schweitzer and R. C. Reardon, 2004), Bugwood wiki archive.” wiki.bugwood.org/Archive:Caterpillars/Macaria_sexmaculata (accessed 2026-11-09)
- Natural Resources Canada, Canadian Forest Service, “Green larch looper, Trees, insects and diseases of Canada's forests.” tidcf.nrcan.gc.ca/en/insects/factsheet/9077 (accessed 2026-11-09)
- iNaturalist, “Macaria sexmaculata taxon page (order and family).” www.inaturalist.org/taxa/224261 (accessed 2026-11-09)