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Maine can expect to see more invasive species

It is expected that some organisms, especially those that are naturally adapted to a wide range of conditions (this includes most invasive species), will be quite resilient to the challenges that a warming climate poses to many of Maine’s native species. Indeed, invaders may even be able to exploit these new conditions to their advantage. Any forecast of the future carries with it some uncertainty, but the scientific consensus is strong on the following point: in Maine’s new warmer, more extreme-weather-prone climate, there will be winners, and there will be losers. Science tells us that the most adaptable species–including those we now consider most invasive–will rank high among the winners.

What invasive species will Maine's changing winters bring?

In areas where winter has historically been consistently cold, such as Maine, minimum winter temperatures are tremendously important biologically, providing natural protection for native plants and animals (including us!). As growing seasons shift and the climate warms, plants and animals, including invasive species, that were once prevented from becoming established here due to Maine’s cold winters, will no longer be constrained.

This climate-driven range expansion is already happening (e.g. think deer ticks and possums) and the implications for all of Maine’s native ecosystems are very serious.

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At the same time as northerly species are leaving the state, more southerly species  such as bobcats, deer, and red-bellied woodpeckers, tufted titmice, opossum, gray fox, and arctic fritillary are expanding their range northward into Maine.

How are aquatic plants species being effected? 

Invasive aquatic plant species such as water hyacinth (Eichhornia crassipes) and water primrose (Ludwegia grandiflora), for example, once thought to pose minimal threats to Maine’s lakes, ponds and rivers due to their cold-intolerance, are both expected to be able to thrive here within a few decades. According to scientists at UMass Amherst and UNH there are hundreds of other new plant species (both terrestrial and aquatic) headed our way. Not all will pose serious risks to Maine’s native ecosystems and economy, but as the climate shifts, we can certainly expect the list of plant species that do pose such risks, to grow significantly.


Source: Water Hyacinth by Dawn McDonald on Unsplash

Aquatic Plant Species


Maine’s lakes are at a higher risk of infestation of aquatic invasive species (AIS) than ever before, in part due to warming temperatures and reduced ice cover. Lake Stewards of Maine (LSM) is a statewide organization which plays a pivotal role in AIS prevention and early detection through educating, training, and mobilizing volunteers to assist with aquatic plant screening survey and mapping efforts.

LSM’s “The Battle For Big Lake” is a compelling 20-minute documentary showcasing the Grand Lake Stream community's collective battle against variable watermilfoil, an easily spread aquatic invasive plant. The film emphasizes how climate change amplifies Maine's vulnerability to invasive species and advocates for integrating traditional ecological knowledge with Western science.

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Get involved by joining LSM’s volunteer programs! Receive free training as an invasive plant patroller and contribute to the fight against Aquatic Invasive Species. For more information on volunteer opportunities, email LSM at

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How are Maine's forests being threatened by climate driven-invasive species?

Maine’s forests are important carbon sinks, with leaves drinking up greenhouse gasses through productivity and the woody parts storing carbon in biomass. But our forests too, are being threatened by climate driven-invasive species. Maine’s native hemlock trees, for example, are now threatened by the invasive hemlock woolly adelgid (Adelges tsugae). This non-native insect would not have been able to survive here just a few short decades ago when our winters were more severe. Now, because of Maine’s warming climate, not only is this cold-intolerant invader poised to decimate our hemlocks (and their carbon capturing biomass), it will also further compromise native brook trout habitat. The shade that evergreens such as hemlocks provide along the banks of streams is needed to keep the water sufficiently cool during critical moments in the life cycle of brook trout, such as spawning season in the fall and fry emergence in the spring.


Source: Hemlock trees in southern Maine by Barbara CariddiMaine Public

Hemlock woolly adelgid is only one of the threats to our forests being aided by climate change. Warmer minimum temps and more frequent, more prolonged periods of drought will also benefit emerald ash borers, southern pine beetles, and other serious forest pests.

Forest Clmate-divn Invasiv Species


Ash Protection Collaboration Across Wabanakik

The Ash Protection Collaboration Across Wabanakik (APCAW) is a group of Indigenous and non-indigenous researchers, Tribal members, and forest caretakers working together to bring more awareness of the cultural and ecological significance of ash trees and efforts to conserve them. APCAW continues the initiative set forth by the EAB and Brown Ash Taskforce, which began in the early 2000s to facilitate the collaborative capacity of Wabanaki basketmakers, Tribal Nations, state and federal foresters, and others to prevent, detect, and respond to the EAB.

How are climate-driven invasive pests impacting agriculture in Maine?

Climate-driven invasive pests are also impacting agriculture. The spotted wing drosophila (Drosophila suzukii) is a small, fruit-fly-related invasive insect of Asian origin that can cause devastating impacts on cultivated (and wild) berry and stone-fruit crops.  Spotted wing drosophila (SWD) were first spotted in Maine in 2011 and can now be found throughout the state, though currently their highest numbers are in coastal and southern areas.

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Photo: Spotted Winged Drosophila (SWD)

Though how successfully SWD will overwinter in Maine is still an open question, it appears that individuals may be able to acclimate to colder winters to some degree by wintering over in leaf duff, greenhouses, etc. But this invader too, is susceptible to prolonged cold, and studies have shown that SWD can be killed by short exposures to temperatures below 23°F.  Maine’s warming climate will make it easier for SWD to survive, thrive and do damage in our state.

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Photo: Trap for the Spotted Winged Drosophila (SWD)

Invasive Pests

“Sleeper species," what are they?

Another path to invasiveness is through what are called “sleeper species.”  These are native or non-native “naturalized” plants and animals that, due to the current environmental limitations upon their growth, do not behave in an invasive manner. As environmental conditions shift in response to climate change, however, the new, more favorable growing conditions may prompt at least some of these innocuous species to ‘awaken’ and become more aggressive and/or invasive.

How could invasive marine species impact Maine's commercial fish species? 

According to the Gulf of Maine Research Institute, changes to ocean temperature and circulation could modify the habitats of more than three-quarters of target commercial fish species in the Gulf of Maine, allowing new, invasive species to enter the region.

Marine invasive species are defined as non-native species that cause or are likely to cause harm to ecosystems, economies, and/or public health.  Hitchhiking marine invaders travel and spread by a variety of transport mechanisms, or vectors.  At least 64 invasions have occurred in the Gulf of Maine ecosystem, and more are likely to be discovered. Marine invasive species negatively impact the Gulf of Maine through competitive displacement of native marine species, esthetic impacts, and the fouling of gear.

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Photo: The invasive European green crab population has exploded in Maquoit Bay druing the last few years due to warming water temperatures. Credit: Troy R. Bennett, Bangor Daily News (BDN)

Management of invasive species in the marine environment is a relatively new endeavor, and understanding of how best to respond to this invasion is ongoing. Current regulatory responses are moving toward a more effective management approach that focuses on early detection, rapid response, research, and education. Such efforts may go a long way in increasing understanding of the impacts of marine invasive species, and to  protect Gulf of Maine ecosystems and economies.

Although species shifts due to climate change may be unavoidable, commercial fishers can adapt by catching new species — for example, lobster fishers in Cape Cod have begun selling delicious Jonah crab alongside their lobster catch as it becomes more common in their traps.


"After the success of the Gulf of Maine 2050 International Symposium in November 2019, the symposium leaders collaborated on a Climate Outlook and Action report summarizing the findings of the symposium and how the interdisciplinary themes that were discussed could impact the Gulf of Maine’s environment, communities, and economies in the future."

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Invasive Marine Species

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