War of the Weeds: The Invading Aliens Are Already Among Us

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.

Now a flurry of additional military activity on Guam threatens to open new avenues of dispersal. The Navy and Air Force are planning a multibillion-dollar expansion of their facilities on the island to counter expected increases in Chinese military activity in coming decades. Guam would be our Pacific command post, the central node of a large, busy network of flight paths and shipping lanes, supply routes and troop movements.

If the snakes could clap, they surely would. No law requires shippers -- military or commercial -- to halt the spread of the snake or even to cooperate with inspectors. Compliance is voluntary. The military has been generally cooperative, but dependence on its goodwill is not a viable long-term strategy.

Were the brown tree snake deemed an agricultural pest, it would fall under the federal Plant Protection Act, which would require the military to guard against its spread. The military is bound to protect homeland oranges (and orange growers) from foreign fruit flies, say, but a vertebrate invader that threatens human health, local economies and natural resources gets a legal free ride.

Another problem is funding. Money for snake control and research comes from short-term grants that are inadequate. The Department of Defense could be more generous. The Navy alone boasts a $1.2-billion budget for compliance with environmental laws, and such funds might be applied to the anti-snake effort, if there was a law that required it.

It is tempting to think of alien species as a matter for the departments of Agriculture or Interior to handle, not Defense. But ecological invaders are made mobile by human commerce and transport, activities in which the U.S. military engages more freely and widely than many small nations.

It is the duty of the military, of everyone, to help keep the bad “seeds” out -- whether red or green, whether they sprout or crawl, crash to Earth in flaming titanium capsules or lift gently from a blossom on tiny membranous wings.