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.