An adult browntail moth with an egg sack. A single moth can lay up to 400 eggs, each one a potential caterpillar with toxic hairs. Credit: Courtesy of Allison Kanoti

There are thousands of plants, animals, invertebrates and fish in Maine that have no business being here.

These are the “invasives.” Species that traveled to Maine from other parts of the world by land, sea or air. Then, like uninvited houseguests who know a good thing when they see it, they take up permanent residence in the state, often at the expense of native species. This past year invasive species hampered everything from gardens to recreation in Maine, and climate change continues to create conditions that will allow invasive species to thrive in the state.

Once they are in Maine, invasive species spread without any help from humans. Worldwide it’s estimated they annually damage more than 5 percent of the global economy. Here in the United States, the cost is around $120 billion.

Here in Maine there are no hard data on what invasives are costing the state. But when you look at the damage caused to forests, agricultural crops, fisheries and sea life, it is in the millions and possibly close to $1 billion, according to Gary Fish, state horticulturist with the Maine Department of Agriculture, Conservation and Forestry.

That’s why state and federal agencies track the progress of invasives and take stearn measures to, at best halt that progress and, at worst, mitigate any damage once they are established.

Last spring, officials predicted summer 2021 was going to be a bad one for outbreaks of the browntail moth caterpillars. They were right. Statewide the poisonous, irritating hairs of the caterpillars left people searching in pharmacies and online for anything to cure the painful skin rash caused by the hairs. The outbreak was so bad in some parts of the state it forced the shutdown of campgrounds.

The emerald ash borer is considered one of the most serious invasive species, according to the Maine Department of Agriculture, Conservation and Forestry. It is a threat to all three species of native ash trees in the state. In August after the discovery of the beetle in Cumberland County, an emergency order was issued restricting the movement of ash trees or ash tree products from the area.

A relatively mild winter in 2020 coupled with a dry summer the previous year created ideal conditions for an explosion of the tick population in Maine this past summer. The highest numbers were reported for dog ticks, which are considered a nuisance pest in Maine, unlike the deer ticks which carry and transmit Lyme disease. Deer ticks continued to be a threat in Maine, but their numbers did not explode.

Along the coast the invasive green crabs have decimated much of the native crab population as the green crabs feed on shellfish and outcompete native species.

Warming temperatures in Maine due to climate change are creating ideal conditions for invasives that are already here and for new ones to move in, according to Fish.

“There is no doubt that climate change plays a part in invasive species in Maine,” Fish said. “Things are only going to get worse.”

As temperatures warm in Maine, there are fewer periods of the severe cold that kill off invasives before they can reproduce.

Along the coast, the hemlock woolly adelgid has been found. This aphid-like insect attacks and eats the sap of hemlock trees. As Maine’s weather warms, according to Fish, the aphid is predicted to move farther inland and threaten native tree species.

Early next year the state will update its list of terrestrial invasive species and recommend strategies to deal with them. There are currently 63 species that are under consideration for listing.

“Of those 63, there are five that we consider to be truly climate change affected,” Fish said. “These are species that may not be a problem right now, but likely will be.”

Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.