Our Fellow Immigrants


House mice probably outnumber house rats in this country by about three to one, but since they average only one-half ounce compared with the rat’s twelve ounces, they cost somewhat less than a third of a billion dollars a year to feed. Their debt to man is of somewhat longer standing, however. They seem to have originated in Central Asia at least several thousand years ago, and they moved in on humans way back in Neolithic, mud-hut times. The first ones to reach this hemisphere probably arrived with the early Spanish explorers. They now are comfortably domiciled in every part of it from Alaska to Tierra del Fuego.

A third immigrant rodent that arrived along with the house mouse was what now usually is called the roof, or black, rat. Smaller than the house rat, it too apparently originated in eastern Siberia. It reached the Near East by the time of the Crusades and voyaged to western Europe with returning Crusaders. It had the run of man’s world until the appearance of the modern house rat in the eighteenth century. This close cousin attacks the roof rat on sight, nearly always wins the battle, and has taken over most, though not quite all, the choicer rat quarters provided by man.

The roof rat received the specific formal name, Rattus rattus . The house rat’s formal name, Rattus norvegicus , is as inappropriate as the name of the English sparrow and is a slander on the people of Norway. When the rats first turned up in England in 1728, the Hanoverian dynasty was new and much despised by some Britons. A rumor got started that the new rodent had been seen swimming ashore from the very ship that brought the recently installed George II to the country. For a while the animal was informally known as the Hanoverian rat. But a naturalist named John Berkenhout heard a false rumor that the rat had actually arrived in England along with a shipment of lumber from Norway. He formally proposed the name Rattus norvegicus . The rule of the international system for agreeing on scientific names is that the first one formally proposed for a new species must be given precedence. Berkenhout’s was the first.

Another unadmired animal immigrant also bears the name of a European nation that resents the association, but in this case the country was the creature’s original home. This is Blatella germanica , the German cockroach. Today, a little carelessness in housekeeping in almost any part of the globe is likely to result, when someone suddenly turns on a light in a dark kitchen, in the sight of a number of half-inch-long creatures darting for the nearest crevices. (One of the few places where these creatures are not called German cockroaches is Germany. In the northern part of that land they are known as Swabian roaches. In the southern part they are Prussian; in the eastern part, Russian; and in the western part, French.)

Not nearly so widespread in this hemisphere as the German cockroach but much more damaging where they have appeared are two other immigrant insects—the Japanese beetle and the gypsy moth. In Japan the former is not a serious pest, but it has been very much so here since it established itself in New Jersey about 1910. It apparently arrived in the form of grubs in the roots of imported nursery stock and has gradually spread westward. The gypsy moth, specimens of which accidentally escaped from the custody of a French naturalist who brought them to Medford, Massachusetts, for experimental tests in 1869, is a native of Europe that feeds on the leaves of many kinds of trees.

Another European immigrant introduced by a naturalist a few years later was the carp. The naturalist was Spencer F. Baird, secretary of the Smithsonian Institution, and few secretaries of scientific organizations have earned more bitter denunciation for their efforts. In countless ponds and streams throughout the hemisphere the fertile and adaptable carp have blotted out the native fish favored by sport fishermen. But eventually Baird may be vindicated. If the hemisphere’s human population continues increasing at the anticipated rate, there will inevitably come about the kind of protein shortage that already afflicts much of the Old World, and carp are one of the most efficient organisms known for turning vegetation into protein.

The Americas’ contributions to the rest of the world have been far fewer, but some emigrants have made big impressions. Among the few native North American animals that have taken to life in other lands are whitetailed deer and gray squirrels. A number of the former were turned loose in New Zealand in the hope that they would provide good hunting. Now the New Zealand government provides free ammunition to anyone who will shoot them and keeps a small army of hired hunters in the field in an effort to hold down the deer’s numbers. In South Africa the North American gray squirrel similarly astonished and horrified its sponsors by passing up the local oaks and acorns in favor of orchards, where it has debudded thousands of trees.