LDD moth caterpillar infestation: What you need to know

Last updated June 28, 2021
Reading time: 2 min

LDD moth caterpillars, which can be recognized by their red and blue spots, have become widespread in the city. Although these caterpillars can chew through a considerable amount of plant cover, the caterpillar is not harmful.

The mild temperatures we had this winter and the dry, hot spring have strongly contributed to the LDD moth caterpillar infestation in Montréal and several regions of Québec. However, this insect does not represent a danger to trees or humans. Outbreaks are cyclical and localized on the island of Montréal.

Recognizing the LDD moth caterpillar

LDD moth caterpillars, which reach a length of 40 to 60 mm when mature, have a spongy appearance  —  in French, they are called “chenilles spongieuses” or “spongy caterpillars.” The caterpillars, which are around from mid-April to mid-July, can be recognized by their grey and black bodies with 11 pairs of spots (six red and five blue) as well as its long fur. The caterpillars become moths whose lifespan is from the end of July to the end of August.

How to get rid of the LDD moth caterpillar

For trees that are already infested with caterpillars, there are few remedies other than time. The caterpillars will go into their cocoons in mid-July to emerge at the end of the month as adult moths.

On small trees, you can use the caterpillar biopesticide Btk (Bacillus Thuringiensis Var. Kurstaki), which is available in hardware stores and poses no threat to plants, animals or humans. You can also put duct tape, sticky side out, on the trunk of trees that have not yet been attacked to keep caterpillars from climbing up to the leaves.

A voracious leaf eater that does not harm trees

The voracious LDD moth caterpillar can eat up to a square metre of foliage over the course of its lifespan. It eats mostly leaves, but also the needles of certain conifers. Although the LDD moth caterpillar can strip a tree of its leaves, the damage is essentially esthetic. There is no danger to healthy trees. They will produce new leaves over the summer; after a few weeks, the damage won’t be apparent. You can help affected trees to produce new leaves by watering them regularly, particularly during periods of drought.

The city is not taking action to control caterpillars on public property (parks, green spaces, etc.) However, affected areas are closely monitored in order to plan for actions that may be needed over the next few years. In the event that the same areas are affected several years in a row, the city will make sure that trees are not damaged or weakened, since they are already affected by many other factors.

Avoid touching caterpillars with your hands. Although they are harmless to humans and pets, their hairs can irritate your skin or even cause certain people to have an allergic reaction.