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Entomologie: the most popular questions

Please find below the topics our entomological information staff is most questioned about. Feel free to continue reading and searching our Insects and other arthropods section to find out more.


Will the caterpillars in my tree kill it?

Despite their sometimes voracious appetite, caterpillars very rarely endanger the survival of the trees and plants they live on. This common belief is due to the fact that a few species are the exception to this rule, and all the other harmless caterpillars are lumped together with them. Some species, such as the eastern tent caterpillar (Malacosoma americanum), the forest tent caterpillar (Malacosoma disstria) and the northern tent caterpillar (Malacosoma californicum pluviale) are gregarious and can seriously damage (usually aesthetically) their hosts. Despite their gregarious behaviour, these tent caterpillars do not necessarily kill their hosts. However, they do weaken them, making them more vulnerable to insects and diseases.

Most damage is aesthetic. A plant whose leaves have been chewed on by caterpillars may be less attractive, but its survival is in no way at risk. As well, over the course of evolution, plants have developed a number of coping strategies, such as increasing the process of photosynthesis that makes them grow, thereby producing more leaves.

The most commonly found caterpillars in our gardens are both spectacular and harmless. If we share just a few of our resources, we are rewarded with a stunning display (metamorphosis).

Here are just of few of the caterpillars you may see: the black swallowtail (Papilio polyxenes asterius), the Canadian tiger swallowtail (Papilio canadensis), the small white (Pieris rapae), the polyphemus moth (Antheraea polyphemus) and the unusual cecropia moth (Hyalophora cecropia). Caterpillars on a plant offer a wonderful opportunity to observe the life cycle of these insects through the seasons: egg, caterpillar and finally, the adult butterfly. In addition to the wonder of seeing them take flight once they reach adulthood, these insects are a food source for other animals such as birds, other insects and small mammals. They play an important role in the balance of natural ecosystems!

To learn more about these insects, consult the Insects and other arthropods section.

Are there more wasps this year than usual?

Every year near the end of the season, people think that there are more wasps than the year before. It’s impossible to say for sure if there are more… or fewer! In fact, what we see at the end of summer and beginning of the fall is the peak of the population, at a time when they are most active and therefore noticeable.

Colonies of social wasps disband completely each year until the workers die in the first frosts. Only new queens will survive the winter by hiding wherever they can – holes in the ground, between layers of tree bark, etc. When spring arrives, young queens look for a place to build a nest alone and do the work to build their colony (building the nest, laying eggs, hunting, and rearing their larvae). As summer progresses, the number of adults in the colony increases more and more rapidly. At the end of the summer, there are many more wasps in the same colony than at the beginning. Each year, this life cycle makes it seem like the number of wasps has suddenly skyrocketed and that they are everywhere.

To learn more about wasps, consult the fact sheet on social wasps and hornets in the Insects and other arthropods section.

There are ants in my house; will they destroy my home by eating the wood?

As surprising as it may sound, it is "normal" to observe ants of different species inside the house in the spring and at the beginning of the summer. They are looking for food sources with the least amount of effort, and a house they can enter (through cracks, holes in screens, etc.) is the ideal place. As the weather grows warmer and more food sources appear outside, they are less frequently seen inside.

The best thing to do (and this is easier said than done) is to fill the spaces through which they enter (cracks in the foundation, holes in screens, gaps in door and window frames, etc.)

You can tell whether ants are living in your house by their presence (activity) in wintertime and by the presence of winged ants (the ants that reproduce).

That being said, you should make sure the ants in your house are indeed carpenter ants. There are more than 100 species of ants in Québec, only five of which are carpenter ants. Carpenter ants cannot live in healthy, undamaged wood – wood that is free of humidity. Despite their reputation, ants of this genus (Camponotus) are often the symptoms of a humidity problem rather than the problem itself.

No matter the species you’re dealing with, to fix the problem, you must destroy the queen. Finally, if you decide to call an exterminator, be sure the exterminator is a member of the Association Québécoise de la Gestion parasitaire (AQGP).

To learn more about ants, consult the fact sheets on ants in the Insects and other arthropods section.