Life in America is being changed by biological newcomers: killer bees migrating northward from Mexico, Dutch Elm disease sweeping through the East and Midwest, Mediterranean fruit flies invading California orchards, the African-born AIDS virus causing a national health crisis.
Stories about such problems surface almost daily in the news, but it has not yet quite dawned on the general public that these various isolated happenings are part of a larger pattern -- a huge global march of animals, plants, insects and microorganisms. Nature is on the move.
Not all biological migrants cause problems: among the other recent arrivals you may see in the course of an ordinary day could be the Holstein cow grazing contentedly in a pasture, the ornamental plant in your garden, the tropical fish in your aquarium and the vegetables on your dinner plate.
The scope of this other migration is so vast that nobody really has any idea of its full size. It is partly accidental and partly deliberate, partly legal and partly illegal. It is a byproduct of many activities, from food production to scientific research to zoo keeping to home gardening. And it is not just a matter of things coming into the United States: American conservationists are worried about the Southwestern cactuses, rounded up by "cactus rustlers" and exported, and about Montana eagles that end up being used in falconry by Saudi Arabian princes.
Although governments make valiant attempts to control biological migration, they have even less luck with it than they do with the human variety. The Dutch Elm disease, for example, arrived in the United States in logs imported for elm veneer, completely undetected. The medfly came stowed away in some imported fruit.
Officials are becoming almost obsessively vigilant against further incursions, but despite their best efforts new fruit flies keep turning up in California. Recently scientists identified eight different kinds in Southern California. They had come from all over the world.
One of the reasons foreign fruit flies find life so congenial in California is that the state is home to so many foreign fruit trees.
Imports beget new imports. Chinese elms are being planted all across the country as substitutes for the more vulnerable native American elms. Insects are frequently imported to help combat exotic weeds, as Greek weevils are now doing with Middle Eastern star thistles in the Pacific Northwest.
As international trade and travel expand, so does the movement of all kinds of living things from seeds to full-grown animals. In recent years, modern animal breeding has become increasingly global: frozen bull semen is shipped around the world to fertilize cattle with the genes of prize bulls, and now the frozen embryos of cattle are also an important item in international commerce. The offspring of a bull and a cow in, say, Denmark, can be removed from its natural mother before birth and shipped to South America to be implanted in a cow of an entirely different breed. One scientist remarks, "You can ship 2,000 cows under your airport seat."
Also, as people move they tend to take their favorite food crops with them. In the United States, new crops of foods favored by Vietnamese and Latin Americans are being grown alongside the "traditional" crops such as peas and lettuce that were imported by earlier generations of human immigrants. The plants themselves are not considered a problem, but there is always the chance that parasites or diseases may come with them.
Biological migration can cause two kinds of problems: ecological upsets in the places the migrants come to, and genetic depletion in the places they come from.
Some plants and animals are exported in such volumes -- such as the more than 200 million bulbs of the popular Snowdrop flower shipped from Turkey in the last decade -- that they become endangered species at home.
RTC As governments and conservation organizations move to control such trade, smuggling, of course, increases: the international trade in contraband birds, cactuses, tropical fish and rare pets has increased greatly in volume and profitability in recent years.
This global biological migration, like the human migrations and globalizing economy of which it is a part, shows no signs of easing up. As an American scientist recently put it, "We're all exchanging our diseases and insects." We are also exchanging our trees, flowers, birds and animals, and in the process creating a different, more biologically homogeneous world.
Walter Truett Anderson is the author of numerous books on the environment, including "To Govern Evolution." He wrote this commentary for Pacific News Service.
And Now, Biological Migration