As the warmongering aliens of "War of the Worlds" infest your local movie theater, keep your eye on the other alien species on the screen, the one those dastardly aliens have brought along in their space pods: the creeping, crimson "red weed."
In the original book, H.G. Wells envisioned the weed as a sort of kudzu on steroids -- leafy, not unlovely, and wildly flourishing. Steven Spielberg's version is more neon and goop. Either way, the red weed embodies an apparently cosmic truism about ecological invasion: rats -- even extraterrestrial ones -- carry fleas.
Increasingly, as we humans move around the world, we are those rats, carrying plants and animals with us and releasing them to new habitats where, often enough, they crowd out native and endangered species and become costly nuisances. The zebra mussel, introduced to North America from Europe in the 1980s by way of ships' ballast water, has altered aquatic ecosystems and become an expensive scourge to industrial intake pipes in the Great Lakes and Mississippi River regions. Gorse, a Mediterranean shrub, is a hard-to-control weed in the Pacific Northwest and New Zealand. The giant African snail, innocuous in its home range, is an agricultural pest on islands throughout the Pacific.
But the red weed carries another lesson about ecological invasions, one all the more pressing in our security-attuned climate. Invading species ride with military traffic and ambition. Consider the Australian brown tree snake, a bird-eating snake that reached Guam by hitchhiking in military gear returned to U.S. bases there during and after World War II. It now exemplifies the damage that one invader, freed from its usual predators and competitors, can wreak in a new environment.
Once, Guam was a snake-free island rich in bird life; today it hosts more snakes per square mile than anywhere on Earth, and the birds, evolutionarily unadapted to predators, are all but gone. The snakes inflict their mildly venomous bite on people, and cause scores of expensive power failures by wrapping themselves around power lines and crawling into transformers.
And they are spreading. Stowing away in cargo that still radiates from Guam, they have turned up in Texas, Japan, Spain and Saipan. Several have reached Hawaii (home to more federally listed bird species than any other state), evidently by crawling into the wheel wells of outbound airplanes. U.S. Agriculture Department inspectors and snake-sniffing dogs work to check outgoing cargo on Guam, but the task is immense and their quarry is, well, snaky.
