The cold, damp and rainy start to June could mean fewer itchy rashes in the weeks to come.

Such weather is ideal for the proliferation of a fungus that can knock back browntail moth caterpillar populations.

Browntail moth caterpillar. Maine CDC

Thomas Schmeelk, an entomologist with the Maine Forest Service, said he saw many caterpillars that had been killed by the fungus Monday as he was observing conditions at Eagle Island off Harpswell.

And while islands have micro-climates that may not be replicated on the mainland, the three days of steady rain that started Friday may have produced the right conditions to curtail populations of the pesky caterpillars, whose near-microscopic hairs cause an itchy rash when they contact human skin.

“It’s not a guarantee, but the rains are coming at just the right time,” Schmeelk said. “We could see the impacts of this weather as soon as next week.”

Damp, wet weather can cause the fungus entomophaga aulicae to spread, infecting and killing the caterpillars. While they are vulnerable to other predators and viruses, the fungus is one of the most common ways their populations are reduced.


The rains have to occur at the right time, however. When it rains in April, the caterpillars are still protected in their winter nests. If it’s rainy in late April and early May when the caterpillars are starting to emerge, the timing might still be wrong for killing them off in large numbers, he said.

However, Schmeelk said, when the caterpillars are larger – as they are now – the fungus is more effective at reducing populations.

Climate change may be contributing to the proliferation of browntail moths, with long-term trends of longer, drier summers and drier springs creating conditions that benefit the caterpillars. Whether the wet early June provides some relief won’t be known for another week or so.

The forecast is calling for more rain in the next few days, although not as much as over the weekend.

A low pressure system lingering on the East Coast is causing “unsettled showery conditions with highs in the 50s and 60s and lows in the 40s through the week,” according to the National Weather Service in Gray. More sun and higher temperatures are expected this weekend, with temperatures in the low 70s on Sunday.

Schmeelk said larger browntail moth populations have been seen in parts of Waldo, Androscoggin and Penobscot counties, but populations in Cumberland, Sagadahoc and Kennebec counties have been smaller.


Browntail moth caterpillars tend to populate fruit, oak, birch, elm and poplar trees.

This is the eighth year of a major browntail moth outbreak that began in 2015 in Maine. Typically, outbreaks last 7-12 years, but the impact of climate change is a wild card that makes it hard to predict when this one will end, according to scientists.

While a rash similar in intensity to poison ivy is the most common symptom, some people who breathe in the hairs may suffer respiratory problems as well. The hairs are difficult to see and can penetrate clothing.

For those who do come into contact with caterpillar hairs and get a rash, many pharmacies sell a compound that can alleviate the itchiness.

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