During the 1970s and 1980s, it was found in numbers sufficient to cause concern in the western states of California, Utah, Oregon and Washington as well as in British Columbia. These occurrences were caused by the transportation of egg-laden materials from eastern sources. British Columbia therefore now faces the threat of gypsy moth introductions from sources to the east, south and west. In masses ranging from about 15 to over 40 mm in length, containing up to 1000 eggs. Shape is usually roughly oval and slightly raised, distinct from the spherical shape of spider egg masses.
Color is buff to beige due to covering of hairs from the female, fading with age to dirty white.
Laid indiscriminately on objects such as tree trunks and branches, rocks, buildings, vehicles, outdoor furniture and, with the Asian race, on stored containers and ships near shore. Egg masses of the Asian race are more commonly found on tree leaves. Usually found feeding on tree foliage or, in early instars, hiding in shady spots. Adults can be found just about anywhere when abundant. One generation of the gypsy moth occurs annually.