Maine is home to a long list of unwanted plants and animals that damage ecosystems and the economy, and pose a risk to public health. Many of these invasive species might live right in your backyard. But would you know if you saw one?
This week, during National Invasive Species Awareness Week, it’s a good time to learn.
But first, what is an invasive species?
An invasive species is an organism — plant, animal, fungus, etc. — that is not native to the location where it’s spreading. Plus, it causes significant damage by degrading wildlife habitat, affecting industries or threatening people’s quality of life.
“Our state parks and public lands, our farms, forests and water bodies are all being damaged by invasive species,” Amanda Beal, commissioner for the Maine Department of Agriculture, Conservation and Forestry, said in a recent statement about the weeklong event. “Everyone acknowledges that we can and should do more to help, and National Invasive Species Awareness Week is a perfect time to learn how to prevent and manage invasive species.”
Maine residents can help fight the spread of invasives by working with their town conservation commission, local land trust or garden club to raise awareness, locate certain species and remove them. In addition, residents can
report invasive species to Maine’s four natural resource agencies through a variety of avenues.
To get you started, here are just a few invasive species, distinctive in appearance, that are easy to spot in Maine.
Credit: Courtesy of Maine Department of Agriculture, Conservation and Forestry
Japanese knotweed grows in dense stands that reach up to 10 feet tall. Many people mistake it for bamboo because it has thick stems that are jointed and hollow. However, unlike bamboo, Japanese knotweed has large semi-triangular leaves that alternate on the stem. The plant also produces spikes of small, white flowers.
There are no similar species in Maine.
Native to Asia, the plant was introduced to the U.S. sometime during the late 1800s as an ornamental plant. It grows extremely fast, pushing out other plant species, and is now widespread throughout areas of Maine that are developed or have a history of human development.
Hemlock woolly adelgid
Credit: Aislinn Sarnacki
An insect that feeds on
hemlock trees, the hemlock woolly adelgid resembles a tiny cotton ball. To find it, look underneath hemlock branches, where these pests cling in clusters as they suck sap. Their feeding causes the tree’s needles to dry out, fade to grayish-green and drop from the tree. The damage can eventually result in the tree dying.
This insect was accidentally introduced from Japan to Virginia in the early 1950s and has since spread north to Maine and south to Georgia. Known populations in Maine are currently confined to coastal regions of the state. To
prevent the spread of this pest, the state of Maine has established a quarantine on hemlock plants or products in all of York, Lincoln and Sagadahoc counties, as well as parts of Androscoggin, Cumberland and Kennebec counties.
To report hemlock woolly adelgid sightings, contact the Maine Forest Service at 207-287-2431.
Credit: Courtesy of the Maine Department of Agriculture, | Maine Department of Agriculture, Conservation, and Forestry
A bane to Maine trail builders, Japanese barberry is a fast-growing, hardy shrub that can be found in forests, forest edges and fields. Covered with barbs, it grows up to 6 feet tall and wide, and is known for clogging recreational trails and taking over fields. Plus, a study shows these plants make
good habitat for disease-carrying ticks.
“It’s an arching shrub that doesn’t look like a raspberry or blackberry or any of the sort of typical brambles,” said Nancy Olmstead, an invasive plant biologist for the Maine Natural Areas Program within the Department of Agriculture, Conservation and Forestry. “It has a distinct profile … and it has little red fruit that looks a little like Tic Tacs. They hang down below the stem.”
In Maine, it has no look-alike.
Credit: Courtesy of Maine Department of Agriculture, Conservation and Forestry
Both lovely and destructive, purple loosestrife is a tall, showy wildflower that’s native to Europe and Asia. In Maine, this hardy perennial edges out other plant species as it spreads, disrupting ecosystems. It especially affects wetlands, stamping out plant diversity and degrading the habitat for wildlife.
Purple loosestrife grows to be 4 to 6 feet tall. Its pink-purple flowers are arranged on tall, crowded spikes. In Maine, the native fireweed plant is a look-alike species. However, if you look closely, purple loosestrife flowers have five to seven petals, while fireweed flowers are larger and have four petals.
Emerald ash borer
Credit: The Maine Department of Agriculture, Conservation and Forestry
A shiny green beetle, the emerald ash borer is an extremely destructive forest pest that was
first discovered in Maine in 2018 in Madawaska. Since then, the insect has been confirmed in three towns in southern Maine as well. The beetle’s larvae burrow and feed under the bark of ash trees, which can eventually kill the trees.
There are many ways to detect emerald ash borers.
Signs of their presence include D-shaped exit holes in ash tree bark and S-shaped tunnels or scarring under the bark. Another sign is woodpecker blonding, which is when woodpeckers remove strips of outer bark looking for the larvae rather than drill deep holes.
The larvae are cream-colored, and the adult beetle is emerald. In Maine, the tiger beetle is a look-alike, but has bigger eyes, longer antennae and legs and a slightly different shape to its body. If you think you’ve spotted an emerald ash borer, you can report it at
maine.gov/eab or to the national emerald ash borer hotline at 1-866-322-4512. Asiatic bittersweet
Credit: Courtesy of the Maine Department of Agriculture, Conservation and Forestry
A common sight along some of Maine’s major roadways,
Asiatic bittersweet is an invasive vine that climbs and twines around other vegetation for support. Entire plant communities can be covered and destroyed by this vine, which can actually cause large trees to collapse.
“It’s easy to recognize when it’s really abundant and doing its strangle-the-tree thing,” Olmstead said. “But it can be tricky when the vines are really small.”
Maine is home to a few other vines that are not considered to be invasive, including native and non-native grapes. However, grape vine bark usually has a peeling, shredded appearance, while Asiatic bittersweet has furrowed bark that doesn’t appear to be peeling.
With a metallic green body and shiny copper wings, the Japanese beetle is a flashy bug that’s hard to miss. It’s oval shaped, with six small white tufts of hair along its sides, just under the wings. But don’t let its decorative appearance fool you. This beetle causes big problems for gardeners.
You’ll often find it feasting on rose bushes. But it has also been found gnawing on foliage of more than
400 different ornamental and agricultural plants, including apple trees, beans and raspberries. Now common throughout Maine, this beetle is here to stay. Reporting these beetles isn’t necessary, but you can try to manage them using traps and other management strategies. Browntail moth
Credit: Courtesy of the Maine Forest Service
Accidentally transported from Europe to Massachusetts
in 1897, the browntail moth has only recently become a big problem in Maine, establishing populations in coastal towns such as Harpswell. This invasive species is both a public health concern and a forest pest. The caterpillars feed on a range of plants, and they have barbed hairs that break off and float through the air, causing many people to develop rashes and headaches. These hairs can also cause respiratory issues.
Fortunately, they’re relatively easy to identify. The caterpillar is dark brown with white stripes along both sides and two red-orange dots on the back. And the moth (or adult stage) is pure white with with a tuft of brown hairs at the tip of its abdomen.
The caterpillars overwinter in nests that they build on the tip of tree branches.
“Now is the time to cut them out and dispose of them so they don’t emerge in the spring as caterpillars with toxic hairs,” Olmstead said.
The safest way to dispose of a nest is by placing it in a bucket of soapy water. You can report these nests by filling out and sending in a Department of Agriculture, Conservation and Forestry
winter web survey form, and you can report browntail moth sightings through another online form, both available at maine.gov. Reporting invasive species in Maine
There are many other invasive species that are affecting Maine’s ecosystems, including invasive
marine animals such as the green crab, and invasive freshwater fish and aquatic plants.
If interesting in learning how to identify more invasive plant species in Maine, check out the
Maine Invasive Plant Field Guide, published by the Maine Natural Areas Program. There’s also a gallery of invasive plants on the Maine Natural Areas Program website.
In addition, the Maine Natural Areas Program tracks invasive plant distribution and management using the online mapping tool called
iMapInvasives. Maine residents can sign up to record their findings using this tool as well, and be notified if invasive species are found in certain areas.
For quick access to many online resources about Maine invasive species and how to report them, visit
This year, National Invasive Species Awareness Week Part I runs Feb. 24 to Feb. 28, with Part II running May 16-23. Learn more at