Hairs from the caterpillars are toxic for humans,[5] causing a poison ivy-like itchy rash of up to sometimes weeks-long duration due to mechanical and chemical irritation.

[9] The species overwinters communally as larvae within a tough, silken tent constructed around branch-tip leaves and anchored to twigs.

In areas where the species is abundant, these tents are a familiar sight, and can be seen on a huge range of plants, especially in late fall and winter when unaffected leaves have fallen.

[10] Charles H. Fernald and Archie H. Kirkland recount historic mentions of brown-tail moths dating back to 1500s, describing outbreaks in Paris, London and Berlin so severe as to completely strip all trees of leaves.

[1] The brown-tail moth is an invasive species in the United States and Canada, having arrived in Somerville, Massachusetts, circa 1890 and becoming widespread there and in neighboring Cambridge by 1897.

[12] The white-winged adults are nocturnal and strongly attracted to light; a report from 1903 likened their appearance around streetlights as being akin to heavy snowfall.

[13] In the United States, many species of birds prey on the winged adults, including English house sparrow and blue jay.

[1] A review of mortality causes in England and mainland Europe described the brown-tail moth as undergoing periodic population outbreaks, each developing rapidly and lasting for several years, followed by a decline to relative obscurity.

[14] A more recent review, conducted in Spain, identified 17 species of parasites, viral diseases, unspecified predation and other, unknown, causes of death spanning from eggs not hatching, during summer, winter and spring as larvae, finishing with pupae failing to produce winged adults.

Generally, mortality increased with population density, although in outbreak regions there was some compensation by females laying 21.6% more eggs (cause not discussed).

)[2] An older review describes other fly species that were confirmed as brown-tail moth larvae parasites, then released in U.S.: Apanteles lacteicolor, Metrous versicolor and Sturmia nidicola.

[16] It, and other descriptions, confirmed that loose hairs can break off and cause very itchy rashes on contact with skin, as well as breathing difficulties similar to asthma if inhaled.

Shed hairs blow about, and can be brought indoors on clothing and shoes, so rashes can occur without the victim coming in direct contact with the caterpillars.

[3][5] A related species, mistletoe browntail moth (Euproctis edwardsi), has been reported as causing a similar rash in Australia, in people working at or visiting a community center, attributed to caterpillars feeding on a tree outside the building.

Non-specific host plant feeding combined with its tendency to reach extreme outbreak densities makes this species a major pest of fruit orchards, ornamental trees and hardwood forests.

[13] Partial list of plant species: apple, cherry, beach plum (Cape Cod, Massachusetts), beech, elm, grape, hops, maple, oak, pear, raspberry, rose and willow, and even conifers like spruce and hemlock.