Background. The Browntail Moth (BTM, Euproctis chrysorrhoea) is an invasive pest from Europe that was first discovered in Massachusetts in 1897. It rapidly expanded its range by 1913 to include all the New England States, New Brunswick and Nova Scotia. Thereafter, its population gradually fell such that by the 1960s it was limited to parts of Cape Cod and a few islands in Casco Bay. This decrease was likely due to natural predators whose numbers increased in response to the increase in the BTM population. Recently, BTM’s numbers and distribution have increased dramatically. Although, the reason for this increase is unclear, it most likely reflects a decrease in the predator(s) that controlled the BTM population throughout most of the 20th century. The ultimate control of the BTM population will depend on re-establishment of the normal ecological balance that existed until recently.