Gypsy Moth

The European Gypsy Moth (Lymantria dispar dispar) is an invasive forest pest that was introduced accidentally in the United States in 1869. Since then, the Gypsy Moth has expanded its range over much of the eastern United States and Canada. It was first detected in Ontario in 1969 and has quickly spread across southern Ontario over the next decade. It is now well established throughout southern Ontario and as far north as Sault Ste. Marie.

Gypsy Moth Cycle

Gypsy moths spend the winter as partially developed larvae in eggs. The eggs hatch in the spring and the young larvae begin feeding by cutting small holes in the surface of leaves. As the larvae develop, they feed on the edge of leaves. Larvae have five pairs of blue and six pairs of red spots along their backs. Feeding is normally completed by early to mid-July.

Pupation occurs in a cocoon which can be found on a variety of surfaces including trees, rocks, houses, boats, trailers, fences, picnic tables, and firewood. In 13 to 17 days, the moths emerge. Both sexes have wings, but only the males can fly. The male moth is dark brown to beige, medium-sized, and is a very erratic flyer. The female is mostly white and has a wingspan between 60 to 70 mm. The female lays eggs in masses of 100 to 1000 on tree trunks, branches, houses, fences, etc. as well as under rocks and forest floor debris. The eggs are covered with fine brown hairs from the female’s abdomen. The egg masses will remain all winter and caterpillars will hatch in the spring, from late April to mid-May.

Close up of Gypsy Moth Larva

Photo credit: Ontario Ministry of
Agriculture, 
Food & Rural Affairs

Close up of 3 Gypsy Moths

Photo credit: K. Shea, Penn State University

Pupation occurs in a cocoon which can be found on a variety of surfaces including trees, rocks, houses, boats, trailers, fences, picnic tables, and firewood. In 13 to 17 days, the moths emerge. Both sexes have wings, but only the males can fly. The male moth is dark brown to beige, medium-sized, and is a very erratic flyer. The female is mostly white and has a wingspan between 60 to 70 mm. The female lays eggs in masses of 100 to 1000 on tree trunks, branches, houses, fences, etc. as well as under rocks and forest floor debris. The eggs are covered with fine brown hairs from the female’s abdomen. The egg masses will remain all winter and caterpillars will hatch in the spring, from late April to mid-May.

How does the Gypsy Moth affect our urban forest?

Gypsy moth larvae or caterpillars will feed on tree leaves. If the larvae population is high, they can defoliate whole trees and forests in a short amount of time. Gypsy Moths prefer oak trees, but will feed on a variety of hardwood tree species. Under normal circumstances, defoliation caused by Gypsy Moths won’t kill a tree. However, trees can decline to the point of death in some cases when defoliation is coupled with dry hot summers, or impacted by other forest pests like Spring or Fall Cankerworm.

Recent signs have pointed to the possibility that Gypsy Moth activity may be on the rise in certain parts of the City of Hamilton. Residents in the Dundas and Ancaster areas became concerned in 2016 about an increase in defoliation, which was attributed in part to Gypsy Moth activity, prompting surveys of the pest.

Gypsy Moth surveying has been underway since the winter of 2016 with the completion of egg mass surveys. An increase in egg masses suggests a coming season of increased pest activity. The monitoring initiated in late 2016 was focussed within the Dundas Valley and into Ancaster, with some areas investigated in west Hamilton. Results of the Gypsy Moth survey suggest that the population will increase in coming years. High impact areas are expected to be within Dundas’s downtown, the Dundas Driving Park, Pleasant Valley, and suburbs within Ancaster. The results also suggest that expanded monitoring is warranted to see if this is a trending increase in the population.

Gypsy Moth Monitoring Map

In 2017, the City of Hamilton will continue to monitor Gypsy Moth populations through the installation of sticky bands and pheromone traps on trees as part of an Integrated Pest Management program. These installations will be focussed throughout Dundas and Ancaster, and will be monitored daily. Surrounding areas will be visually inspected on a weekly basis by Forestry staff, including Flamborough, rural Ancaster, and west Hamilton.

In addition, individual trees within Dundas Driving Park (Dundas), and Somerset Park (Ancaster) will be treated with a naturally occurring bio-pesticide, Bacillus thuringiensis kurstaki (Btk). This pesticide does not affect people, pets, birds, or bees.

Homeowners are encouraged to monitor their hardwood trees like oaks, maples, beech and walnut for the presence of Gypsy Moth larvae. Please help save trees by:

  • Installing Sticky bands to monitor and control caterpillar populations.
  • Installing Pheromone Traps in trees to lure and trap male moths to prevent them from mating with female moths
  • Contacting an Arborist if you think a tree on your property is being heavily defoliated by Gypsy Moth.
  • Contacting the City of Hamilton at 905-546-CITY (2489) if you think a tree on city property is being heavily defoliated by Gypsy Moth. 
  • Watering your tree and trees near your home in the public right-of-way once every 3 to 5 days during periods of high heat or drought

Consult your local Nursery or Hardware store for Sticky Bands and Pheromone Traps.