Invaders TitleNYSM home

The World at Risk

Invasive species are not only a problem in New York state— they are a problem worldwide. As residents of New York state, we contribute, accidentally or on purpose, to that problem.
Just as people have brought invaders here for centuries, people have moved plants and animals native to New York state and North America across our country and around the globe. We are both the victims of, and the cause of, the spread of invasive species.

Black Cherry
Barbara Tokarska-Guzik,

Black Cherry

Prunus serotina
Black Cherry is native to the United States. It was first brought to western Europe in the early 1600s as an ornamental plant. Since then, it has been planted widely in eastern and western Europe as an ornamental and as windbreaks in forest and open agricultural areas. Local spread is from seeds dispersed by fruit-eating birds and mammals.

Black Cherry can shade out the growth of native ground vegetation and hinder regeneration of native forest trees. The leaves it drops may be allelopathic and can poison livestock.

Pine Wood Nematode

Pinewood Nematode
William M. Ciesla, Forest Health
Management International,

Pinewood Nematode

Bursaphelenchus xylophilus
Pinewood Nematode is a microscopic roundworm native to the United States. It was first detected in southern Japan in 1905. It was probably introduced in a shipment of timber or packaging material. It has since spread into Taiwan, South and North Korea, and China.

It attacks the vascular tissue of pines native to Asia, which can result in pine wilt (a non-native disease) and the death of infected trees within one year. In Japan, as many as 20 percent of the trees in some forest stands have been killed as a result of this introduced species.

The Pinewood Nematode has a high reproductive rate and can survive extreme conditions, such as drought, low temperatures, and lack of food. In North America, most native species of conifers are resistant to the wilt disease.
Grape Phylloxera
Ohio State University, Ohio Agricultural Research and Development Center

Grape Phylloxera
Whitney Cranshaw, Colorado State University,

Grape Phylloxera

Daktulosphaira vitifoliae
Grape Phylloxera is an aphid native to eastern North America. In the 1860s, it was introduced in France, probably attached to the root stock of imported American grape vines. The native European grape vines were very susceptible to the insect. By the end of the 1870s, 60 to 90 percent of European vineyards were destroyed. How did the French wine industry bounce back? They grafted the naturally aphid-resistant roots of North American stock onto their stock.
Blue Gill
© 2002 John White


Lepomis macrochirus
The Bluegill is a popular game fish native to parts of eastern North America. In New York, it is native to the Allegheny and St. Lawrence Rivers but has been introduced statewide. In fact, it has been introduced worldwide. As it grows, its diet becomes increasingly dominated by small fish, and the Bluegill is now recognized as a major threat to biodiversity in many areas.

In 1960, the mayor of Chicago gave the fish to the crown prince of Japan as a gift. The crown prince brought it home with good intentions. Japan was having a protein shortage. What happened? The Bluegill has become invasive in freshwaters of Japan, reducing the numbers of many native fish.
Gray Squirrel
© 2007 Joyce Gross

Eastern Gray Squirrel

Sciurus carolinensis
The Eastern Gray Squirrel is native to the eastern United States north into Canada. It was introduced in several areas of the western United States and in Europe. It can be quite successful in a variety of habitats. It is now the most common squirrel in many urban and suburban areas in the western United States.

It was accidentally released from the London Zoo and was introduced to Italy as pet in the 19th century. In England, because it has few natural predators, coupled with its high reproductive rate, its population spread rapidly. It can now be found in England, Ireland, and northern Italy. In Europe, it competes with and often displaces the native Red Squirrel. It is also destructive to native trees.
© 2004 Tom Greer,


Lithobates catesbeiana
The Bullfrog is native to central and eastern United States and southeastern Canada. It was introduced in the early 1900s to the western United States. It was accidentally introduced during trout stocking of waters. It was also intentionally introduced as game (for food), released from aquaria, and used for pest control. It was introduced in Hawaii, Mexico, the Caribbean, South America, Europe, and Asia.

The Bullfrog is an opportunistic predator on aquatic, terrestrial, and flying invertebrates and vertebrates. The Bullfrog competes with and preys upon a variety of native species.
Opossum Shrimp
NOAA, Great Lakes Environmental Research Laboratory

Opossum Shrimp

Mysis relicta
The Opossum Shrimp is native to deep glacial lakes such as Lake Champlain, Lake George, and the Great Lakes. It was introduced to lakes in the western United States and Canada as a prey species for trout and other game fish. It is an opportunistic feeder on zooplankton and may compete with young trout for food. In some areas where it has been introduced, it may substantially alter the aquatic community—particularly native zooplankton. This, in turn, is thought to have affected the growth and survival of game fish.
Potato Beetle
David Cappaert, Michigan State University,

Potato Beetles

Colorado Potato Beetle

Leptinotarsa decemlineata
The Colorado Potato Beetle, originally native to Mexico, moved into the Great Plains following the spread of its host plant, Buffalo Burr. After the introduction of the potato (which is native to South America), the beetle switched to feeding on this new host (potatoes). Feeding mainly on potatoes, but on other crops as well, the beetle has expanded its range. It is now found throughout much of North America and has also been introduced to Europe.

The Colorado Potato Beetle can defoliate an untreated potato crop. It is a serious pest of potato and eggplant, and an occasional pest of tomatoes. So, in the United States, it is a native species feeding on an introduced species. In Europe, it is an introduced species feeding on another introduced species.