The range of the gypsy moth spreads throughout North America, Europe and Africa. An invasive species in the eastern United States, it is one of the most destructive pests of hardwood trees. Its larvae voraciously consume the leaves of over 500 species of trees and plants and, in 2015 alone, the species contributed to the defoliation of over 60,000 hectares in Massachusetts.
In the 1860s, a French scientist inadvertently introduced gypsy moths to Medford, Massachusetts. He was attempting to see if the caterpillars could be used in the commercial silk trade when some escaped. By 1889, the town was plagued – there are reports of caterpillars completely covering houses and sidewalks and of residents hearing them munching away throughout the night. Since then, the species has continued to spread and today is found throughout the eastern and northern US – the moth’s larvae can be carried by the wind and can be spread at a rate of 20km a year.
There are several natural and introduced predators that keep gypsy moth numbers somewhat in check: the white-footed mouse, which consumes larvae nesting near the ground, certain species of insect-eating birds and a species of imported Japanese fungi (Entomophaga maimaiga). Introduction of the parasitic tachinid fly (Compsilura concinnata) in 1906, specifically to control the gypsy moth in the US, resulted in the near extinction of many other moth species.
Over the past 20 years, swathes of US forest have been sprayed with pesticides in an attempt to control the seemingly relentless advance of the gypsy moth. This obviously has its own environmental implications but as research to control the species over the last 100 years has yielded very few results and the moth continues to wreak havoc on the forests of the US, there seems to be no other option at present.