Fall webworms vs Tent Caterpillars

We have been getting a lot of inquiries about the nests that we are seeing in many of our trees right now, with concerns that these are tent caterpillar nests.

Our Parks staff have informed us that these nests are actually from an insect called fall webworms.

Fall webworms are a native insect in this region. They make a similar nest as tent caterpillars but with a couple of differences: the nests appear later the season, and the nests expand so they can feed inside the protective nest. Usually they cause little lasting damage to the trees. The webworms are consuming leaves, and while this is somewhat stressful to the tree, the growing season is nearly finished for the year, and the leaves will grow back next year.

There are limited tools to get rid of fall webworms from trees, and removing them may end up doing more harm than good.

One method that is used for tent caterpillars is to spray a biological insecticide – actually a bacteria – called BTK. This bacteria would coat the leaves on which the caterpillars would then feed. However, this solution is less effective on fall webworms because the leaves they are consuming are inside the protective webbing and the BTK can’t reach the leaves.

Another potential solution for removing the webworms is pruning them out of the tree. Our Parks staff advise that this option is generally much more stressful for the tree than having the leaves consumed. The tree will grow new leaves again next year, but pruning material out of the tree may remove branch tissues that have taken the tree several years to grow, and would take the same amount of time to replace. So although the webs in the trees might look like they are very stressful for the trees, they generally don’t cause lasting damage.

Find out more about fall webworms:https://tidcf.nrcan.gc.ca/en/insects/factsheet/8125
*Photo from Natural Resources Canada

City of Courtenay

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You can read the whole argument at: https://www.researchgate.net/publication/340538684_This_civilization_is_finished_Time_to_build_an_ecological_civilization

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