Our Fellow Immigrants

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Even more unwelcome abroad has been a little native American beetle with bright yellow and black stripes down its back. When first noticed early in the last century, it was a species of some rarity, apparently confined to the eastern slopes of the Rockies and to a diet of the leaves of such weeds as the beaked nightshade. White potatoes belong to the nightshade family. The first taste of leaves of potato plants put out by settlers persuaded the bugs to abandon the weeds, and the location of their first enthusiastic attack on potatoes in the early 1860’s won them the popular name, Colorado potato bug. The nutritious new diet fed a population explosion among the beetles; by 1865 the first hordes had reached Illinois, and by 1874 others were on the Atlantic coast and seeking new frontiers.

Their first foray into Europe was in 1877, when a small number were found in Belgium. That advance party was wiped out. For half a century stringent measures similarly destroyed every other beetle beachhead. World War I weakened these defenses and gave the creatures a foothold in France. They slowly fought their way eastward, and their successful invasion of Polish and Russian potato fields after World War II led to Russian charges that the United States was waging underhanded biological warfare.

A number of western hemisphere plant emigrants have been received more enthusiastically. North American tobacco, Central American sweet potatoes, and pineapples from South America were early successful emigrants to the Old World. Many kinds of beans—lima beans, string beans, pea beans, kidney beans—were under cultivation from Peru to New England when Columbus arrived, and they quickly caught on in one place or another abroad.

Next in importance to potatoes among western hemisphere gifts to the rest of the world is corn. Columbus took seeds to the eastern hemisphere on his first trip back, but corn was a long time winning acceptance there. The Elizabethan historian of exploration, Samuel Purchas, quoted an early traveler in Africa who had described seeing corn growing in a Portuguese colony there and remarked: “They make no account of it for they give it to their Hogs.” The observer was hasty with his no-account. Corn’s great virtue is precisely as a livestock feed. About eighty-five per cent of the crop in this country usually goes to hogs, cattle, and chickens, and our enormous corn harvests are among the chief reasons for our plenitude of meat. In the last few decades the rest of the world has come to understand this, and corn acreages have been increasing everywhere.

But cases like that of the starling in this country and the white-tailed deer in New Zealand have shown that a good thing in one place is not necessarily a boon somewhere else. Nowadays men tend to be far more cautious than they once were in helping other species migrate from one part of the globe to another. Some authorities argue vehemently in favor of the most rigid international quarantines of all forms of life, and a number of laws aiming at this goal have been passed by the United States Congress and other legislatures.

The difficulty about such laws is that few would-be migrants take the trouble to find out whether the trip they have in mind is legal. The most rigid exclusionists admit that it is scarcely possible to make absolutely certain that bacteria, fungi spores, and other microscopic forms of life will stay where they belong or go back where they came from. Realistically speaking, it is only the larger, more readily noticeable species of insects, crustaceans, fish, birds, and mammals that they can hope to keep put. Even this hope is often vain.

Ten years ago a Florida bird-watcher took pictures of some strange birds that had landed in his pasture. It took him a long time to get them identified. They were African cattle egrets. Their ancestors a generation or two back had in some unknown way crossed the Atlantic and settled down. They still are multiplying rapidly and now range all along our Atlantic coast.

Advocates of stringent quarantine darkly insist that it is too early to be sure that these birds will not have a disastrous effect on the balance of nature here. Others admire the egrets’ enterprise and take comfort in the evidence that the effect of Homo sapiens and his fellow immigrants on this hemisphere has not yet rendered it utterly repugnant to all other forms of life.