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Description: The heavy, flightless, 50 mm (2 inch) long female moth is white with a yellow to buff abdomen and irregular blackish bands on the forewings. The male moth is active during the day, searching for females. The male is smaller than the female and mottled brown and black. The eggs are deposited in 20 to 40 mm (3/4 to 1 1/2 inch) masses of 100 to 700 eggs, covered with bright yellow to buff velvety scales from the female's abdomen. Older egg masses become bleached as they weather. Fully-grown gypsy moth caterpillars are 40 to 65 mm (1 1/2 to 2 1/2 inch) long, hairy, and vary from slate-gray to a sooty or dusky color. The caterpillars have five pairs of blue spots followed by six pairs of red spots along the back, which distinguish the gypsy moth caterpillar from other defoliating caterpillars. The head capsule is black and gold.
Life Cycle: The female lays her eggs on trees, stones or fences, under loose bark, and in other protected places in mid- to late summer. The eggs overwinter and hatch in early May, when Amelanchier spp. (serviceberry, shadbush) blooms. The newly-hatched caterpillars spin silken threads on which they may be wind-borne for long distances. In mid-summer (six to seven weeks), mature caterpillars spin a few strands of silk and pupate within a dark brown pupal case. The moths emerge in one to three weeks (males first). There is one generation a year. Damage: Vigorous hardwoods can usually survive one complete defoliation, but a similar attack may be fatal to conifers. Repeated defoliation of hardwoods, however, will reduce tree vigor to a point where other factors or pests may cause death. Tree losses have been noted after one to two years of complete defoliation during drought periods, particularly on poor sites. The aesthetic, recreational and watershed values of forest, park and ornamental trees can be seriously threatened by the gypsy moth. The hairs of the young larvae often cause a skin rash on humans. Control: A fungal disease caused by Entomophaga maimaga has controlled the gypsy moth in recent years throughout most of its range in the United States and further controls have been unnecessary. Natural: Gypsy moth infestations are regulated by many factors, most important of which is stand composition (hosts). Gray birch and chestnut/white oak stands are favored for initial buildup, whereas maples are not. Persistently low winter temperatures (-20 degrees F/ -29 degrees C) may cause egg mortality in unprotected situations. Populations may be reduced by birds and mammals. There are also a number of parasitic or predatory insects which attack gypsy moths, including Calosoma beetles, and some species of parasitic wasps and flies. Cultural Control: Stressed trees are more vulnerable to damage from defoliation. Keep trees in good health and vigor. Maintain good soil nutrient and moisture relationships by mulching, watering, judicious green wood pruning, and fertilizing when needed. Replace susceptible species of low commercial or aesthetic value with resistant species. Create mixed plantings with species not generally fed upon. Quarantine: It is very important that gypsy moths not be spread to areas outside of the northeastern states. Gypsy moths are commonly transported in the egg or pupal stage on home and yard objects, mobile homes, trailers, etc. There is a USDA-APHIS regulation prohibiting the transportation of gypsy moth-infested items. Chemical: Chemical control is not presently warranted against this insect.
Adapted from G.R. Nielson, University of Vermont Extension, 1999
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