Warning: The back half of this paragraph may creep you out a little bit. The brown tree snake has a bad reputation, and it’s really earned one. As one of nature’s most storied invaders -- they’ve had two books published on them in recent years (here and here), and I’d say they’re about due for a major motion picture. Brown tree snakes are nocturnal, fairly aggressive, mildly venomous, and semi-aquatic. And according to their growing folklore on the island of Guam, they’ve been known to curl up in the toilet (picture here) and nip at peoples’ rear ends at a particularly vulnerable moment.
The brown tree snakes have completely taken over on Guam. Believed to have arrived from the Admiralty Islands, New Guinea, or Australia in the holds of post-World War II cargo ships, the snakes conquered an ecosystem where there were no natural enemies. They ate every bird egg available; now Guam is a tropical paradise with almost no tropical birds. The snakes have also devoured native geckos, lizards, and other reptiles. There are an estimated two million brown tree snakes living on Guam’s 136,000 acres. They outnumber people by about twelve to one. About twenty years ago, they started causing regular power outages by shorting themselves out on the island’s antiquated electrical grid.
Thanks to the snake, Guam’s ecosystem is largely a write-off. But this nuisance species has also made sea or air travel a nuisance: Every cargo container, every airplane wheel well, and every corner of every ship or aircraft leaving Guam has to be scoured for stowaway snakes trying to leave Guam the same way they arrived. Personnel from the U.S. Animal and Plant Health Inspection Service (APHIS) patrol docks and runways, deploy search dogs, and otherwise stay vigilant (on our dime) to make sure that Guam’s tragedy isn’t repeated elsewhere in the Pacific. In 2004, Hawaii Congressman Ed Case said that APHIS stops between 6,000 and 7,000 stowaway reptiles a year.
Like Guam, Hawaii has no natural predators for the snakes, and would be particularly vulnerable to a snake-based ecological disaster. Guam-to-Hawaii flights have reported several snakes-on-a-plane in recent years, but it’s believed Hawaii remains un-colonized.
The saga of the brown tree snake is an almost inevitable result of global commerce. Asian Longhorn Beetles are native to China, and since the late 1990s they’ve hitchhiked on cargo ships to infest trees in the U.S., Canada, and Europe. The beetles bore holes and lay eggs in hardwood trees -- mostly poplars, maples, willows, and elms. Once infestations are discovered, the trees have to be taken down. First spotted in Brooklyn in 1996, the beetles soon showed up on Long Island, in New York’s Central Park, New Jersey, New England, Chicago, and Toronto. Infestations were also reported in the UK, Austria, and Germany. APHIS has experimented with insecticides and fungi to try and kill the beetles off, but one of the most effective tools has been tree-listeners. Yes, people who listen to trees. Hearing the telltale buzzing from a tree is the only sure way for early detection of a beetle-infested tree.
There’s a waterborne invader that’s not only an ecological threat, but it’s downright bizarre. The Asian Carp has colonized the Illinois River. Asian carp are big fish -- twelve pounds or more, with a record size of about 60 pounds. They’ve literally eaten the other fish’s lunch in the Illinois River, and they’ve done the same thing in the Mississippi system, having likely gotten their start on catfish farms, where they were imported to eat algae. Here’s the bizarre part: Asian carp go nuts when they sense the noise and vibrations of boat engines, and can propel themselves ten feet or more out of the water. Take a boat on the Illinois River, particularly in the spring, and there’s a good chance you’ll be hit upside the head by an airborne 12-pound fish. CBC reporter Mark Stevenson tried this a few years ago.
Should the carp jump their way into the Great Lakes via the Chicago River, they’ll likely share the water with another invader. Zebra Mussels are native to the Caspian Sea, and arrived in the ballast water of ships. The first North American colonies were found near Detroit in 1988. Zebra mussels have pretty shells, and are about the size of a fingernail. They love fast-moving water, and gravitate toward intake pipes for factories and power plants. By the early 1990s, they were causing small-scale industrial disasters throughout the Great Lakes. This map traces the zebra mussel sightings from the Lakes to the Hudson River, down the Mississippi to New Orleans, and up the Tennessee and Arkansas Rivers as well. While there’s little good to be said about the first three invaders here, zebra mussels have a beneficial side: They’re voracious filter feeders, and have actually helped clean the water in infested areas. Great Lakes fish like yellow perch and the smallmouth bass may actually benefit from sharing the Lakes with these invaders.
None of these stories are new, but after many years, they’re still developing. But they’re all cautionary tales for how easy it is for global commerce and transport to blow some pretty big holes in the web of life.