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Pam Hoffman

caterpillers on tri colored birch tree

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They are gypsy moth caterpillars Pam. The paired red dots one part of the body, paired blue dots on the other are definitive. Not desirable as caterpillar or moth. They have been spreading west across the continent for 70 years and can explode in numbers, defoliating large treed areas - they eat many tree species. Depending on where you are in North America, government-run control may be in play with the Extension service or Agriculture department keeping tabs on where they are reported, mapping hot spots and directing hatching-time aerial spraying of a bacteria that infects caterpillars. There is another biological control, a fungus that infects and kills them. It was released decades ago as a natural control and seemed for many years to have been ineffective but now seems to be established and effective (https://www.canr.msu.edu/news/gypsy-moth-outbreaks-in-michigan).

Report them - one route is via the invasive species network


Kill what you see - they can be squashed, or since they migrate down the tree trunk daily, then back up to eat leaves, a sticky trap around the trunk catches and immobilizes them. Search for products such as Tanglefoot. Learn to recognize the later-summer egg masses and destroy them to reduce next year's population. Healthy trees can usually survive defoliation one year, especially late in the year but repeated defoliation can kill.

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