You’ve probably noticed these creepy cocoons in the trees, which seem rather prolific, particularly this time of year.
According to the Ontario Ministry of Natural Resources (MNR), they are webworms, and the good news is that they are harmless.
Fall webworms are not to be confused with eastern tent caterpillars or forest caterpillars.
According to the MNR, several caterpillars produce large amounts of webbing in trees. Eastern tent caterpillars are active in early summer, while fall webworms feed in late summer. These caterpillars will become moths in their adult phase. The forest tent caterpillar is another type of “tent caterpillar” in Ontario, but it does not produce large, noticeable tents in the forks of trees like the eastern tent caterpillar.
Tent caterpillars make their cocoons in midsummer, while fall webworm cocoons are formed in the fall. Right now, residents may be seeing the newly opened cocoons of eastern tent caterpillars, which are now in their adult phase. Cocoons of fall webworms will become more noticeable as fall progresses.
Populations of these caterpillars are cyclical, increasing and decreasing over time. Tent caterpillar outbreaks occur about every ten years and sometimes last up to two years. The fall webworm population is typically high for two or three years before returning to lower levels. Caterpillar outbreaks often end due to increased predation and disease.
Outbreaks of fall webworm typically have little effect on tree health because the damage occurs at the end of the growing season. Tent caterpillars seldom kill infested trees, but they can reduce a tree’s health since they feed earlier in the growing season. Healthy trees can handle minor damage. However, according to the Ministry, repeated defoliation can weaken trees, making them more susceptible to other forms of stress.
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