It’s the stuff of science fiction flicks – a species multiplying without restraint until it covers the earth. In one version, insects with no natural enemies soon devour all the plant life on the planet. Or the reverse, a plant extends its tendrils around all other living things, slowly smothering them to death.
Luckily, when plants and animals evolve in a particular habitat together, each species has its own control in the form of other plants or animals that keep its growth within bounds – as long as man doesn’t interfere.
But it seems to be the nature of mankind to always want to improve things just a little. Sometimes we do it by accident, but as often it’s a purposeful intrusion. And sometimes the result is havoc.
Driving our motorhome through the South we saw the results of one such effort to improve on nature. Along the roadsides we noticed a distinctive type of topiary, one that imitated the outlines of trees, fences, deserted houses, and telephone poles. But a closer look showed that it wasn’t just imitation; underneath the greenery were the disintegrating remains of the original patterns, creations of man and nature that had been engulfed by the ever-expanding growth of a plant called kudzu.
Kudzu didn’t occur there accidentally. It was imported from the Orient during the late 1800′s. At first it was used merely as an ornamental vine that would quickly cover an otherwise unattractive visage. But then Southern farmers discovered that this fastgrowing plant not only provided forage for their animals, but it grew just about anywhere. With government encouragement they planted kudzu on farms and along roadsides to prevent erosion. And it got out of control.
Today kudzu is a pest, claiming vast areas of the countryside, stretching out its tendrils at a rate of more than a foot per day, expanding like a green tide and covering everything in its path. During the spring and summer it adds an attractive tropical green to roadsides and abandoned fields, but when the first frost comes it turns an ugly brown. It’s now a part of our scenery, for better or worse.
Kudzu is just following the example of many other introduced species. Whether plant or animal, when any species is placed into a hospitable environment with no competition and no enemies, it will crowd out the natural inhabitants. This has happened a number of times in the past. In fact, some of the introduced species in the United States have been around so long that they are now considered part of our natural surroundings.
Ask the average person what the most common bird is, and they usually answer “sparrow.” Press them further, and if they know their birds at all, they reply “house sparrow.” There are other birds that occur in greater numbers, but as its name implies, the house sparrow lives around houses, around cities, around human habitation. Therefore, we see lots of them.
But the house sparrow is not a native North American bird. It was introduced into the United States at Brooklyn, New York, in the middle of the 19th century. This feisty creature shows little fear of man, and even less for other small birds. More prolific than many native birds, the house sparrow has taken over most of the available nesting sites near farms and towns, resulting in the decline of some other birds, the bluebird being a notable example. The house sparrow’s success has been stupendous, and this is the case for many other transplants.
The same thing results whether the release of a non-native species is purposeful or accidental. The gypsy moth that devastates the eastern forests was not released intentionally. A French naturalist brought the caterpillar of the gypsy moth to the United States in 1869 trying to introduce a silk industry. Some of the moths got away, and they have been expanding ever since, devouring forest foliage as they extend their range.
A more recent insect pest causes aggravation across many southern states – the fire ant. These insects came from Brazil as stowaways on a cargo ship, and first appeared in Mobile, Alabama, in 1918. Considering an ant’s lack of transportation facilities, the fact that it spread to nine states in a little more than 50 years was just short of miraculous. Millions of dollars have been spent trying to stop the ants from building their plow-breaking mounds and biting both man and beast. So far, the ants are winning.
Perhaps the easiest place for an alien species to establish itself is in the state of Florida. With a mild, humid climate many species survive there that would die in the cold of a northern winter or the dryness of a southwestern summer. But in Florida exotic species have become a fact of life.
In 1966 the giant African snail was introduced into Florida. The fact that it was done by a 10-year-old didn’t make the problem any less serious. Growing to 12 inches and two pounds, the snails started raiding vegetable gardens, nibbling on ornamental plants, and even chewing the paint off of houses. It cost almost $1 million to get rid of them.
The importation of pest species is a real problem – not just over the international boundaries, but within the United States as well. There’s a reason for the agricultural inspection stations on the borders of states such as California and Arizona, and for the questions asked by border inspectors of visitors to Mexico and other foreign countries.
The men and women who work at these border stations are just trying to keep undesirable species from spreading, to keep our country from becoming the stage set for a sci-fi series. And as frequent travelers, we can help them do their jobs.
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