The brown-tail moth was accidentally brought to Massachusetts about 1890, and since that time has spread from near Boston, where it was first observed, to Maine and Nova Scotia on the northeast, central New Hampshire on the north, the Connecticut River on the west, and to northeastern Connecticut on the south. It has also been found in other parts of the country on imported plants, but so far as known, these cases have all been immediately discovered and the insects destroyed. Colonies which originated in this way are likely to be discovered at any time, however, and in any case a general distribution of the pest over at least the eastern United States is almost certain to occur sooner or later.

The adult moth is pure white, except at the end of the body, which bears a tuft of golden brown hairs, which has given the insect its name. It measures about an inch between the tips of the extended wings, and flies at night during the first half of July. The moths are active and are attracted to lights, and may often be seen clustering around street lights. They lay their eggs in clusters on the leaves of trees, mingled with brown hairs from the end of the body, which conceal the eggs themselves, and an egg cluster may contain from 200 to 400 eggs. These hatch during August, and the little caterpillars feed in company, and when abundant may skeletonize the leaves, causing them to turn brown.

In September each cluster of caterpillars passes to the tip of a twig and here spins a web, drawing together a number of leaves for the purpose. These webs or nests of silk and leaves are quite small, being perhaps three or four inches long, and generally an inch or two across, and are very tough and resistant to attempts to tear them open. In these tents the caterpillars winter, leaving them as the buds open and the leaves begin to grow in the spring. The caterpillars now scatter in all directions, feeding on the buds and leaves, and become full grown about the middle of June. They then pupate among the leaves, and from these pupae the moths appear in July.

The caterpillars are quite general feeders, but their favorite food plants are perhaps the fruit trees, the oaks, maples and elm. Two reddish spots on the back, one behind the other and not far from its hinder end, make the recognition of this caterpillar easy.

Besides the injury to the trees which this insect causes, it is the source of much discomfort and even of suffering to persons where it is abundant. The caterpillar bears numerous finely barbed and brittle hairs, some of which, at least, are also poisonous, and when the caterpillars molt, pupate, or the adults escape from the pupa, these hairs seem to become liberated and are carried by the winds. When the hairs strike the human skin, they appear to work their way into it and produce a severe irritation known as the "brown-tail rash." Cooling mixtures may be used to relieve this, such as Menthol, Zinc oxidi, Aq. calcis, Acid carbolici, 10 grains 2 drama 8 ounces 15 drops

To control the insect, use is made of the habit of the caterpillars of wintering in colonies together in webs or nests at the tips of the twigs, these being cut off and burned at any time during the late fall or winter. When the caterpillars are feeding, either during the early fall or in the spring, spraying with arsenate of lead is a quite effective method of control.