Officials issue warning as dangerous insects reemerge in massive numbers — here's what you need to know

An invasive caterpillar species is chowing down on the trees of Michigan as part of its multiyear life cycle, and it needs to be managed sooner rather than later.

What's happening?

Spongy moth caterpillars reemerged this spring in Michigan, where they cluster on oak trees and other deciduous species, eating their leaves and leaving them vulnerable to other pests and diseases, per ClickOnDetroit. Debris from their activities and droppings can create a nuisance for people, and their hairs are potential irritants to humans as well. 

They spread partly by the wind blowing small caterpillars to other trees or humans moving their egg clusters on firewood from place to place, as the Michigan State University website detailed. 

Why is this invasive species important?

Spongy moth caterpillars feast on hundreds of species of trees, according to the U.S. Department of Agriculture, making ample opportunity for other pests to move in and cause damage, on top of other stress conditions that can leave numerous dead trees in their wake. 

The current generation is part of the outbreak that began in 2019, according to ClickOnDetroit. In 2021, they did 1.3 million acres of damage, declining to 386,000 in 2022, which is a significant drop, but populations will collapse from a variety of factors for 8 to 12 years before popping back up, so management is crucial.

Invasive species like this caterpillar can reduce biodiversity by ousting native species for resources, or in this case, reducing the availability of resources and habitats by killing trees. The loss of trees also hurts the larger environment by lowering the ability of plants and forests to do things such as trapping carbon. 

There's also the negative impact on the economy. According to the National Invasive Species Information Center, invasive alien species cost the global economy at least $1.288 trillion over 50 years, leading up to a 2021 report. That's an ironic number to consider when the spongy moth caterpillar was brought to the U.S. in the 1860s by naturalists trying to breed a sturdier silkworm, according to the Connecticut Department of Energy & Environmental Protection. In a shipment with some French silkworms, the spongy moth caterpillar hitched a ride and has been in the U.S. ever since. 

What's being done about the spongy moth caterpillar?

According to ClickOnDetroit, the Michigan Department of Natural Resources first recommends non-pesticide means of control and management for the caterpillar. The department recommends keeping an eye out for egg clusters and scraping them into buckets of soapy water, as well as sweeping grown caterpillars into soapy water.

You can also make a trunk trap by tying a burlap band around the trunk of trees you want to protect. Pesticide is a last-ditch option, and the DNR recommended seeking professional help for especially difficult infestations.

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