The phrase "invasive species" calls to mind a plant or animal being imported from Europe or Asia and running wild in North American habitats. The likes of starlings and garlic mustard cause major problems for our native wildlife and for wildlife managers. Sometimes the invasion works in reverse. One example is the gray squirrel, which was brought to England over a century ago. In this country, they are an occasional pest for homeowners and bird feeders but otherwise harmless; in the United Kingdom, they threaten the native squirrel population.
The Lake District, in the north of England, is on the front lines of a new Hundred Years’ War. It is a war between rodents. Since the 19th century, gray squirrels, an American import, have been overtaking Britain’s native red squirrels and claiming their territory. The grays have moved up from the south of England, thinning out the reds along the way. The reds now survive mostly in Scotland and the English counties, like Northumberland, that border it. The grays are larger and tougher and meaner than the reds. They can eat newly fallen acorns, and the reds cannot. They cross open lands that the reds are scared of. They are more sociable than reds, allowing for higher population densities. Although gray males cannot mate with red females, they often intimidate red males out of doing so....Read the rest.
The situation has now reached a crisis point: there are only an estimated 160,000 red squirrels left in Britain, whereas there are more than 2 million grays. Without human intervention, reds could be gone from England in 10 years. The red squirrel is a national icon, and the British government is trying hard to save it. Deliberately killing a red squirrel or disturbing its nest, called a drey, is a crime. Last year the government set up more than a dozen refuges for red squirrels in the north of England.