A warming Vermont gives way to more invasive species

BURLINGTON, Vt. (WCAX) - Vermont is known for its snow, but state researchers say the winters aren’t what they used to be. And that change is conducive to invasive species making a new home in the Green Mountains.

“We are also seeing increases in our summer temperatures overall, but also increases in our winter temperatures,” State Climatologist Lesley-Ann Dupigny-Giroux said.

Dupigny-Giroux says it’s no secret Vermont is just getting warmer. The average temperature has gone up about three degrees since 1900. Pests that usually die off in the winter may start to thrive.

“Insects with different lifecycles will be affected in different ways, but in general, warmer is not good for those of us that don’t want to see invasives establish,” said Judy Rosovsky, Vermont’s state entomologist.

Rosovsky says one of Vermont’s greatest protections are deep cold snaps, something the state has lacked in recent years. Experts say the average low in December in the 20th century was about 11 degrees, not quite cold enough to kill a number of species.

“Our whole ecosystem is adapted to cold harsh winters, and the invaders are often vulnerable,” said Rosovsky.

Rosovsky used an increasingly familiar pest, the emerald ash borer, to explain. An experiment out of the Midwest showed at 10 below, they had a 34% mortality rate. We have only hit that once since the start of 2020 and didn’t hit it this past winter.

But killing with cold isn’t the only concern, lengthening seasons is another.

“You push your frost dates back further into the year, you have a longer time for things, insects that are active in the fall to survive,” said Rosovsky.

“We grew up hearing about, ‘Don’t plant before Memorial Day, the 31st of May.’ Part of that was there was a chance of frost to occur,” said Dupigny-Giroux.

Both researchers say those frosts are now shifting, giving bugs and invasives more time to move, or plants more time to thrive. Dupigny-Giroux says pests, tourism, plants and precipitation are all connected, and we have to look forward with that in mind.

“It’s all sort of like mixed in together, like a system, to try to really pinpoint how this all works out,” she said.

Rosovsky says invasives like the spotted lanternfly, a species knocking on Vermont’s door, typically do not like the cold but could find comfort in a warmer state. Ticks like warmer temperatures over freezing, and although not extremely active, they will move and begin to show themselves. A few degrees change in average lows and can make a difference.

Patti Casey, the environmental surveillance program manager for the Agency of Agriculture, says if the state warms, new ticks could be on their way, and with them the possibility of more tick-borne illness.

“We’ve seen a few lonestar ticks, which we consider to be a more southern tick. And we are also keeping our eye out for the Asian longhorn tick, which is an invasive from Australia, I believe, to the U.S., and it’s in more of the southern states. That may be coming, and if our climate is favoring more of those southern species, they very well could take hold here,” said Casey.

But there are a number of factors besides climate that affect population like host species or precipitation. There are also species that die off if it gets too hot, the hemlock woolly adelgid had a high winter mortality rate with cold winters but that rate has dropped as we get warmer. Now summer mortality rates are up, meaning there is some trade-off.

Related Stories:

Entomologists track spread of emerald ash borer

Spotted lanternfly reported in Vermont

Harmful spotted lanternfly getting closer to Vermont; still not here

Tennessee nursery fined for shipping infested hemlocks to New York

Is cold weather ticking off ticks?

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