A major gypsy moth (Lymantria dispar) hatching was observed in spring 2021 in Greater Montreal, notably in Brossard, at Parc des Sansonnets. Native to Eurasia, this caterpillar is fond of oaks, birches and poplars, and can attack up to 500 plant species. It feeds from late May to early July, after which it transforms into a moth. The female lays her eggs on various trees, shrubs and outdoor furniture.
Frequently asked questions
- How to recognize gypsy moths
- Its body is hairy with a double row of five pairs of blue spots, followed by a double row of six pairs of red spots on the lower back.
- Take care! Caterpillar hairs can cause skin irritation or allergic reactions in some people. We recommend wearing gloves when handling the insect.
- Are my trees in danger?
- The gypsy moth causes aesthetic damage by defoliating infested trees. Although it does detract from the beauty of the landscape, healthy trees will survive the attack and re-leaf in the aftermath. In the short term, damage will be minimal.
- Repeated infestations in consecutive years could have more severe consequences. The city is therefore closely monitoring the evolution of gypsy moth populations in Quebec.
- How common are infestations?
- The proliferation of the spongiform caterpillar is attributable to a mild winter and a dry spring. These conditions have favored a resurgence of this species in 2021. Generally speaking, a gypsy moth outbreak occurs every 7 to 10 years. Depending on weather conditions, this problem may not recur.
- How to control gypsy moth?
- Wear gloves to collect them before immersing them in soapy water or crushing them.
- For easy retrieval, wrap a strip of burlap around the trunk of the affected tree. The caterpillar will feed at night and come down during the day to take shelter. Simply remove the canvas and soak in soapy water to remove them.
- Biological insecticide based on Bacillus thuringiensis kurstaki (Btk) bacteria is authorized without the need for a permit, in accordance with current municipal regulations. Application takes place during the caterpillar feeding period, from late May to early July.
- In late summer and autumn, females lay between 200 and 1,000 eggs on tree trunks, under branches, on fences, on outdoor furniture, on trailers and under building cornices. Dislodge the egg mass and immerse it in a bucket of hot water and bleach or ammonia.
- To help reduce the caterpillar population, we recommend removing eggs with a stick during the winter season. The latter are easy to spot when plants are leafless. Gypsy moth eggs often hide on tree bark or outdoor furniture. The egg masses are about the size of a dollar coin, and look like small beige or brownish hairs.
Further information