Animal Expatriates

The infamous Colorado potato beetle

The infamous Colorado potato beetle

Animal Expatriates

 So many non-native animals including such notorious ones as the  Starling, the Zebra Mussel, the awful members of the Rattus genus (gray rat and Norwegian rat) and the Burmese python, have become established in North America and are wreaking ecological and economic damage here that we perhaps don’t realize that  the Americas (from Canada through South America) are a potent source of  problem species across the oceans.   Here are eight animal species native to North America that are valued (if not just ignored) on this side of the Atlantic Ocean, but regarded quite differently overseas. A reference for each one is provided to trigger further reading.

The Colorado Potato Beetle (Leptinotarsa decemlineata) first appeared in Europe in the 1870s and spread across the continent over the next 30 years. It is a major pest in European potato fields, especially in Germany. The beetle is native to southwestern North America, including Colorado and Mexico (full original range unsure) where one of its principal hosts is the buffalo-bur (Solanum rostratum), a prickly annual weed in the same genus as the potato. By 1840 the bug incorporated the potato into its range and spread rapidly out of its limited native distribution to become a major pest in central and eastern North America. It can be controlled for awhile with pesticides but quickly develops resistance as it had to DDT in the 1950s. The  beetle got its start in Europe around military bases in France in the first World War, but then spread eastward. It is generally absent from Scandinavia, but widespread in potato-growing regions of Russia.


The American Lobster  (Homarus americanus) have been introduced live into Europe over the last several decades and wild individuals have been repeatedly observed in Norway, Great Britain and other northwestern European countries. More information is needed to clarify whether wild, reproducing populations are established in these countries. Interspecific hybrids involving the European lobster (H. gammarus) occur, and in France, over a thousand were released into open waters although their fate is unclear. The interloper is believed to transmit diseases lethal to the closely related European Lobster, including an epizootic shell disease which could threaten European Lobster fisheries.  A bacterial disease lethal to Homarus spp and native to North America, has appeared in European lobsters in Norway and Great Britain. The American Lobster is larger, more aggressive, more fecund, and adapted to a wider habitat range than the European Lobster suggesting competitive inequalities that could lead to displacement of the native species.

Stebbing, P, et al. 2012.  Reports of American Lobsters, Homarus americanus (H. Milne Edwards 1837), in British waters. BioInvasions Records 1: 17-23.

The North American Bullfrog (Rana catesbeiana) has been widely introduced outside its natural range over the past two centuries including to the western U. S., the Tropics, Europe and Asia.  Introductions continue with several more occurring since the late 20th century. Often frogs are moved around within an occupied area rather than relying on overseas shipments. It is now widespread in Europe, expanding rapidly in southwestern France (where control efforts have been underway) and found in many stations in northern Italy where it got an early start but may be stabilizing its numbers. A major concern relative to American bullfrog invasions is that these animals aymptomatically carry the fungus responsible for chytridiomycosis, a lethal fungal disease that has spread to all continents harboring amphibians  and has severely reduced or even exterminated amphibian populations worldwide. The impetus for this huge range extension of the frog is the flavorful meat of its hind legs! Unfortunately, where escaped, the bullfrog either eats or outcompetes a wide variety of other amphibians, reptiles, and fish and thus is capable of disrupting ecological communities and reducing species diversity in freshwater ecosystems.

 G. F. Ficetola et al., 2006. Pattern of distribution of the American bullfrog Rana catesbeiana in Europe. Biol. Invasions DOI 10.1007/s10530-006-9080-y.

Global Invasive Species Database: Lithobates catesbeianus (=Rana catesbeianus).

The Eastern Grey Squirrel  (Sciurus carolinensis) of eastern North America is a major pest in the British Isles where it threatens the native red squirrel (S. vulgaris). The interloper competes vigorously with the red squirrel for food and carries a harmful squirrel pox disease, which is deadly to the native but asymptomatic in the grey squirrel carriers. The decline of the red squirrel in Britain has been described as “catastrophic” and largely attributable to the invader which is larger, more aggressive and able to eat a wider variety of nuts and seeds.  To add to the impact, forest surveys show that the food trees preferred by the red squirrel (esp. the European larch) are steeply declining in England and Scotland and the species preferred by the interloper (Sitka spruce [another North American import], and planted deciduous tree stands) have increased in area. Grey squirrels were first introduced from the U. S. in the 19th century as pets or as curiosities for the rich. Note that S. vulgaris is not the same species as the North American red squirrel  or chickaree (Tamiasciurus hudsonicus),  a successful species not in decline.


The Raccoon (Procyon lotor) of North America is an adaptable generalist that is at home in the wilderness and in our suburbs. They have charmed many a casual observer, but in the U. S., also act as a reservoir for rabies which can be transmitted to pets and to humans.  In addition, although not native to the Old World, it is established throughout Europe, especially in Spain where there is a thriving population in the central area of the country. In eastern Europe, raccoons infected with rabies have been found and in Germany raccoons host a parasitic nematode that was thought to be confined to North America. Ecological impacts are expected given that predation of native fauna was verified in Spain.

Garcia, J. T. et al. 2012.  Recent invasion and status of the raccoon (Procyon lotor) in Spain. Biological Invasions 14:1305-1310.

The American Mink ( Neovison vison= Mustela vison) is present in the wild in the British Isles, the Scandinavian and Baltic nations, China and Argentina, and several other countries. It is the most frequently farmed animal for its fur and escape from fur farms is the chief mechanism of dispersal in non-native lands.  A voracious predator, it takes a variety of prey, from rabbits to crayfish, including some larger than itself. The American mink is apparently a contributor, in some places a major one, to the near-extinction in the United Kingdom of the water vole, a small native rodent. Studies have shown that in certain areas, the mink can significantly decrease populations of birds, rodents, amphibians and other mustelids (weasels and martins and the European mink).  In comparison to it’s escaped congener, the European mink is smaller and less adaptable and therefore likely to be adversely affected in competitive situations.  

Bonesi, L. and S. Palazon 2007. The American Mink in Europe: Status, impacts and control.


The freshwater Louisiana Crayfish (Procambarus clarkii), native to the southeastern U. S. and adjacent northern Mexico, was widely introduced on other continents largely for aquaculture to provide food.  It has escaped into natural waterbodies, including in American states outside its natural range and widely in the temperate and tropical zones. It eats eggs and fry of native fish, mollusks and other crustaceans. In some places it outcompetes local crayfish and displaces them.  It is also a carrier of a specialized fungus that is deadly to other crayfish. It was unwisely imported into Kenya and South Africa in the 1970s to reduce populations of parasite-harboring snails. Its numbers grew rapidly and its burrowing habit has damaged canals, dams and riverways.

A snail-eating snail looking for prey.

A snail-eating snail looking for prey.

 The Rosy Wolfsnail (Euglandina rosea), an obligate predator of snails, and native to the southeastern U.S. (North Carolina south to Florida and west to Texas), was introduced to the Indian and Pacific Ocean Islands  (including Hawaii) in the 1950s  to control the African Land Snail, another exotic species introduced earlier to the islands to please gardeners. Unfortunately, the Rosy Wolf Snail preferred the small native snails as its prey.  It may now be found in Hong Kong, Taiwan, the Solomon Is., Guam and French Polynesia, as well as India and North Borneo. It is a likely cause of, or at least a contributor to, the extinction of over 130 species of snails native to the oceanic islands it has invaded. If the prey are small enough the wolfsnail consumes them whole including the shell!