Acquatic Invasive Animals

Over the years, many plants and animals have been brought into the US either intentionally or as stowaways in cargo and materials. Without native predators, many of these species out compete native species or reproduce in such a large quantity as to cause environmental damage.

This page describes a number of the invasive animals which can be found in the Adirondacks.

More information about Adirondack invasive species can be found at the web site for the Adirondack Park Invasive Plant Program.


Zebra Mussel / Quagga Mussel

Zebra mussels and the closely related quagga mussels are filter-feeding freshwater bivalve mollusks. Zebra mussels are small, 1/4” to 1 1/2” long, and D-shaped with light and dark brown stripes. The quagga mussel is paler toward the end of the hinge and is slightly larger, about 3/4” wide.


Spiny & Fish Hook Water Fleas

Spiny and fish hook water fleas are tiny crustaceans less than 1/2” long with long, sharp, barbed tails. The fish hook water flea has a more slender spine and prominent S-shaped loop on the tail. Both species collect in gelatinous globs on fishing equipment and lines.


Asian Clam

Asian Clam is a freshwater bivalve mollusk. The outside shells are yellow-green to brown with elevated concentric rings. If the color chips away, white spots can be seen underneath. The inside of the shells may be light purple. Adults are small, usually less than 1 1/2 in length.


Chinese Mystery Snail

The Chinese mystery snail is a large freshwater snail about 2” in length. The shell is smooth, uniform in color, and light to dark olive-green with 6 to 7 convex, deeply indented whorls. It looks similar to the native banded mystery snail.


Rusty Crayfish

Rusty crayfish resemble native crayfish but can be identified by their more robust claws and by the dark, rusty spots on each side of the carapace (upper part of the shell). Native to the Ohio River Basin, the rusty crayfish is commonly sold and used as bait and spread to several states mostly in the Midwest and Northeast. They inhabit lakes, ponds, and streams, preferring areas that offer rocks, logs, or other debris as cover.


New Zealand Mud Snail

New Zealand mud snail is a very small freshwater snail, averaging only 1/5” long. The shell has 7 or 8 whorls with deep grooves and varies from gray and dark brown to light brown. The snail has spread throughout Europe, the Great Lakes, and throughout many Western states. It inhabits fresh and brackish streams and lakes and thrives in disturbed watersheds and along shorelines with silt and organic matter substrates.


Northern Snakehead

Northern snakehead is an elongated freshwater fish 2-3 ft in length with a long dorsal fin, large mouth, and sharp teeth  Snakehead are present in several states in the U.S. In its native range it is found in muddy or vegetated ponds, swamps, and slow-moving streams. It could survive in much of North America if it became established.



Alewife is a species of ocean herring with a bluish-grey to olive back with silvery sides. The body is wide, narrows at the belly, and averages 6“ in length. They have large eyes, a prominent black spot near the gill cover, and a forked fin.


Round Goby

The round goby is a small, soft-bodied fish with a distinctive black spot on the first dorsal fin. They have large, protruding eyes and range in length from 4” to 10”. While juveniles are grey, adult round gobies have grey, black, brown and olive green markings.


Viral Hemorrhagic Septicemia

VHS is a rod shaped fish virus. VHS affects all sizes and ages of many fresh and saltwater fish and has caused severe declines in fish populations of the Great Lakes region and Canada.

Terrestrial Invasive Animals


Emerald Ash Borer

EAB has a golden-green body with dark, metallic green wings and a purplish-red abdomen. Adult beetles average 3/8” to 3/4” long and 1/6” wide. EAB emerges in late spring, flying from June to August.


Asian Long-Horned Beetle

ALB has a glossy black body with white spots on the top of the wings. Adults are 3/4" to 1" long. Antennae are roughly 2 times the body length with distinctive black and white bands. The legs and antennae have a bluish tinge. Adults are present from July to October.


Sirex (European) Woodwasp

Woodwasps (or horntails) are large, fullbodied insects about 1 - 1 1/2” long. Adult females have dark metallic blue or black bodies with orange legs. The male's head and thorax are metallic blue, and the abdomen is orange at the center and black at the base. Adults emerge from July to September.


Brown Spruce Longhorned Beetle

This flattened brown beetle is less than 1” in length and is very similar to native long-horned beetles but has a darker head with reddish-brown antennae about 1/2 the length of its body. They are active June to August.


Balsam Woolly Adelgid

Adults are tiny, about 1 mm long, and appear dark purple to black in color. They produce a thick layer of a light colored, waxy, wool-like material that covers their body.  This insect infests and kills fir trees. North American species are the most sensitive to attack.


Viburnum Leaf Beetle

Viburnum leaf beetle adults are brown and about 1/4” long. These beetles have spread into much of the Northeastern U.S. and Canada, infesting only viburnum plants such as the cranberrybush.


Alfalfa Snout Beetle

The alfalfa snout beetle is a grey, wingless beetle about 3/8” long. The beetle has been most destructive in northern New York and Ontario where it attacks alfalfa, clovers, and other legumes.


Hemlock Woolly Adelgid

HWA is tiny, less than 1/16”; long, and is dark reddish-brown to purplish-black in color. Its name derives from a white ”wool-like” covering called an ovisac on mature egg laying adults. HWA develops and reproduces on all hemlock species but attacks only Eastern and Caolina hemlocks



There are many species ranging from 1” to 2” or more in length. In North America, earthworms are mostly brown or variations of brown and yellow. Since the end of the last great Ice Age, very few earthworms were found in most of North America. They were introduced intentionally by European settlers to fertilize land for agriculture. Now, about 1/3 of the more than 180 species found from Canada to Mexico are invasive.


Feral Hogs

Feral hogs, or feral swine, can include domestic pigs “pet” pigs that have been released or escaped captivity and ”gone wild” wild boar (native to Eurasia) that escaped from licensed shooting preserves, or a hybrid cross between domestic pigs and wild boar.


Sudden Oak Death

Sudden oak death is a plant disease caused by a fungus pathogen. The fungus kills several oak tree species by causing a leaf disease called ramorum dieback. It thrives in cool, wet climates and has been especially damaging along the west coast.


White Nose Syndrome

White nose syndrome is a newly discovered cold-loving fungus that invades the skin of bats, leaving a visible ring of white fungus around the face, ears, and parts of the body.

Updated 3/20/2018