Snakes in the Grass

The night is neither dark nor silent. A full moon looms large and close overhead, shooting shafts of silvery light through the jungle canopy. Suddenly, the chirps of tree-climbing geckos and the rustle of palm trees swaying in humid evening trade winds are joined by the soft sound of footsteps trampling the damp undergrowth.

Two beams of light slice through the brush as biologist Earl Campbell strides forward on a narrow path cut through a tangle of ironwood trees and coconut palms. One light, from his spelunker’s helmet, is fixed on the treetops; the second, from a powerful hand-held spotlight, moves in continuous arcs.

Campbell methodically scans each tree for the invaders that threaten the economic and ecological lifeblood of the U.S. territory of Guam. These intruders are not terrorists, rebels or members of a hostile army. They are snakes. Brown tree snakes. A silent, slithery menace that made its way here just after World War II. Unchecked by natural predators, the mildly venomous nocturnal reptiles quickly infested the island, their numbers exploding almost exponentially. In just four decades, they have devoured most of the native birds and many of the mammals in what was once a Pacific paradise.

Federal wildlife officials have charged Campbell, 29, with finding ways to control the serpents. He is praying that the electrified fence surrounding this grove has rendered at least one 100-square-meter patch free of the unwanted import. For an hour, he has tramped through feathery fronds of tangan tangan trees and wild hot-pepper bushes, seeing only ghostly giant praying mantises and iridescent eyes of fist-sized moths.

Elated, Campbell says to a companion: “We can finally say there is at least one place on Guam that is free of brown tree snakes.”

But minutes later, as he makes his way along the perimeter fence, his lights shine on a telltale shape: a brown tree snake coiled high in a tree. His face falls. He pulls the snake out of the tree and injects it with a heart-stopping drug.

“I guess it’s back to the drawing board.”

THE PEOPLE AND WILDLIFE OF GUAM, A 209-SQUARE-MILE VOLCANIC ISLAND about 1,500 miles southeast of Japan, have survived typhoons, tidal waves and massive earthquakes. They lived through the Japanese occupation of World War II and a weeks-long siege of American bombings aimed at driving those human invaders out. Through it all, they endured.

Now, however, this southernmost outpost of the Mariana Islands chain is facing a biological catastrophe it may not be able to overcome. Brown tree snakes, native to the Solomon Islands and Papua New Guinea, have decimated much of Guam’s animal and avian kingdoms. In the 40 years since they arrived here, stowaways on U.S. military ships, they have wiped out nine of Guam’s 11 native bird species, including the Mariana fruit dove, Micronesian kingfisher and Micronesian honeyeater. The few remaining native birds--including 50 Mariana crows on the endangered species list--cling to existence in nests atop trees that are wrapped with snake-proof electrified wires. The snake also threaten many indigenous lizards and mammals, such as the Mariana fruit bat.

Guam is an extreme illustration of what can happen when a foreign predator gains a foothold in an otherwise balanced ecosystem. Scientists say such alien species are a prime cause of wildlife extinctions around the globe, trailing only habitat destruction by humans in places such as the Amazon rain forest. The trouble is acute on isolated islands where local species have no similar native predators and no room to evade the interlopers.

In most cases, a species’ demise can usually be traced to more than one culprit. Flora and fauna in the Hawaiian Islands, for example, are besieged by feral cats, goats, mongooses, pigs--even mosquito-borne avian diseases--all carried in by human settlers. On Santa Catalina Island, native foxes and birds compete with bison herds, wild pigs, goats and deer, all of which were imported.

In Guam, however, a single voracious interloper species has devastated bird, mammal and lizard species that have had no time, biologically speaking, to evolve evasive behavior patterns.

Brown tree snakes, known in scientific texts as Boiga irregularis , are highly adaptive masters of camouflage that grow as long as 10 feet and will try to eat just about anything. In its native haunts, the snake faces competition: Other snakes and giant lizards eat them and their eggs. Not so on Guam.

“The brown tree snake was liberated in an environment almost equivalent to a biblical land of milk and honey, where there were no enemies and an enormous amount of food,” says Stuart Pimm, an ornithologist and ecologist at the University of Tennessee at Knoxville. Pimm has spearheaded efforts to relocate certain Guamanian bird species, such as flightless rails, to nearby snake-free islands.

The brown tree snake population swelled to a high of 30,000 per square mile in some areas during the late 1980s before exhausting much of their food supply. It has leveled off to the current 12,000 per square mile in some forested regions--still the highest density of snakes in the world. But biologists warn that the population could easily soar again should climate shifts, for example, favor an increase in rodent populations.

“They are the quintessential hidden animal--99 out of 100 tourists visiting an area with 12,000 brown tree snakes per square mile would not even know they were there,” says Gordon Rodda, a herpetologist with the National Biological Survey. “We’ve done visual counts in patches of jungle in Guam gridded with trails and even on the best of nights were only able to spot 8% of the snakes that were there.” To get an accurate density figure, scientists painstakingly mark and count snakes in a fenced-off section of jungle and then extrapolate their data.

Celestino Aguon, a member of the indigenous Chamoru people and a biologist who heads efforts to save the Mariana crow, winces when he recalls how Guam used to be. “In 1978, there were still bridled white-eyes, kingfishers, ground and fruit doves and plenty of flightless rails on this northern part of the island,” Aguon whispers from behind a well-hidden blind at the foot of a 60-foot-tall tree girded by electrical wires. He’s come to check on progress of a mating pair of crows as they build a nest in its boughs.

“Birds began to show a precipitous drop in population and we blamed it on avian diseases, pesticides, even cats and dogs,” he says. “Eventually, we determined it was the snake, although it seemed impossible that a single species could devastate whole species of birds.”

The forest quiet is broken by the call of a crow as it circles ever lower beneath rolling thunderheads, then plunges into a nest Aguon hopes will one day produce a precious clutch of eggs. “Just look at that bird,” he gasps, squinting through a pair of binoculars. “Beautiful, isn’t it?”

Many Guamanians, afraid for their still-thriving tourist industry, downplay talk of the snake infestation. To be sure, Guam’s bays remain meccas for snorkelers, its white sand beaches havens for Japanese tourists. For the casual visitor, there are few signs of the battle against the serpents. Traps set near the island’s international airport and Andersen Air Force Base are difficult to spot--the better to catch the snakes. And Campbell’s experimental fences so far are concentrated in one corner of the island.

But in the the jungle, where birds used to squawk and dart amid the fruit and flowers, the snakes’ legacy is obvious. “Now,” says Pimm, “one feels going into Guam that something is terribly wrong.”

YVONNE MATSON KNOWS THE TERROR OF FINDING A SERPENT IN THE nursery. One morning five years ago, she was awakened by screams from her 10-month-old son, Skyler. She raced into the room and found the baby yanking with his right hand at a snake coiled around his neck while it chewed on a finger on his other hand. The bedsheets were bloody and a powerful musky stench emitted by the excited snake pervaded the room.

“It’s a snapshot imprinted on my brain,” recalls Matson, shivering at the memory as Skyler, now 5, listens attentively in her lap. “I was jumping up and down, screaming hysterically, as my husband unwrapped the snake, flung it across the room and smashed it with a broomstick.”

Skyler was rushed to a hospital, where an emergency room doctor prescribed an antibiotic and sent the family home with assurances that there was “nothing to worry about.” Still, Skyler “couldn’t stand up and his arm swelled up as big as Popeye’s,” she says. “Thank God, within a few days, he was fine.”

Then, four months ago, in a home Matson moved to four years ago, her mother was awakened by a sharp sting on her middle finger. Just inches from her face were the brilliant yellow eyes of a snake, hanging from a wall painting.

“My mother was OK--but she was real upset,” says Matson, who hired a witch doctor to exorcise her home. “I only wonder if I’m next,” she adds, knocking hard on her kitchen table three times.

For years, Guam officials have advised residents to screen windows, crevices, even toilet pipes to keep out the reptiles. More than 100 people have been bitten in recent years--most of them sleeping toddlers and infants. There have been no deaths, but doctors fear that the venom, which can cause a painful swelling in healthy adults, could yet prove fatal to infants.

So far, tourist encounters with the snake have been few, say island biologists and business folk. But on at least one occasion, a brown tree snake slithered down a tree at the Hilton Hotel’s poolside bar, says Thomas Fritts, a herpetologist for the National Biological Survey. In another report, a Navy man was bitten by a snake that came up through the toilet at a military housing complex.

On Guam’s hotel row in Tumon Bay, groundskeepers’ duties include snaring and snuffing out the snakes before guests spot them. “I decapitate them with a jungle knife or spin them in the air and break their neck before they can do anything,” says one Hilton employee, who figures he catches about 20 snakes a month.

A few miles down the road, T-shirt shop owner Paul Guerrero recalls an encounter a few years ago when he found his puppy “screaming bloody murder with a snake coiled around it. I’ll never understand it--the puppy was four pounds and way too big for the snake to eat,” he says. “I shot that snake with my CO2 pistol. It lunged at me and I shot it in the head. Then I got my machete and whacked it.”

Brown tree snakes will try to feed on anything that will fit in their mouths--which open as wide as an open hand--as well as things that won’t. Attracted by the scent of blood, they have one of the broadest diets in the reptile world and readily gobble up ground beef, dog food, barbecued ribs and chicken bones.

Distressing face-to-face encounters are not the only impact the snake has on daily life. Serpents, searching for birds and their eggs in nests atop power poles, trigger massive electrical outages--up to 100 a year as recently as 1992--causing damage to key power grids, computer facilities, even refrigeration units, which results in widespread food spoilage. Utility officials have erected fine mesh fencing around major electrical substations and installed “hot” wires near the tops of vital power poles, but blackouts are still a monthly occurrence.

Experts are hoping to prevent the snakes from spreading to neighboring islands. In Hawaii, officials use trained dogs to sniff the cargo of each plane and ship arriving from Guam. Similar inspections are required before those planes leave Guam. Still, six snakes have been discovered at airports and shipyards in Hawaii in the last 12 years.

“Hawaii is certainly as vulnerable ecologically as Guam and maybe this is parochial pride, but we may have more to lose here,” says Alan Holt, director of science and stewardship for the Nature Conservancy of Hawaii. “If we cannot muster the public will to stop a snake that can crawl up the toilet and bite you or suck an infant’s arm down its throat, what can we stop?”

EFFORTS TO CONTROL THE SNAKE HAVE INCLUDED THE SUBLIME AND THE ridiculous. One idea involved circulating recipes for snake stew. The meal never quite caught on. In the summer of 1990, territorial authorities held a monthlong “sweepsnakes”; the grand prize was a fully equipped pickup truck for the most snakes collected. The event was scrapped the following year when word got out that some competitors might be trying to breed snakes.

Another brainstorm, quickly dismissed by health and sanitation officials, called for splashing cow blood on jungle roads, on the theory that nighttime drivers would run over the blood-sensing reptiles as they bellied up for a slurp.

Some residents suggested introducing mongooses, a cobra-eating Asian mammal. But wildlife experts pointed out that mongooses hunt by day; tree snakes feed by night.

Biologists say that if they had to nominate a single predator from the brown tree snakes’ native range for introduction in Guam, it would be an egg-eating snake. However, there is no guarantee that it would limit its diet: It would probably eat bird eggs as well.

So federal biologists and the Guam Division of Aquatic and Wildlife Resources are trying to create “snake-free zones” by erecting electrified barriers. Of Campbell’s two 100-square-meter test sites, only one has remained snakeless. If they can perfect the fences, they hope to install them around urban and commercial centers as well as critical bird habitats. But first, they must find ways to make the barriers rodent- and weatherproof. Rats have chewed snake-size holes around the electrical wire in some trial fences made of nylon netting, Campbell says. Storms have taken a toll, too. “The barrier can’t be too tall or it turns into a kite in a typhoon.” And the voltage can’t be too high: “A dead snake on a barrier could short-circuit the system,” he says.

Until the fences are fine-tuned, the daunting task of keeping the slithering menace off seaport docks and airport loading zones belongs to Thomas Hall, district supervisor in charge of animal damage control for the U.S. Department of Agriculture.

Hall trains Jack Russell terriers to sniff for snakes in and around aircraft. There also are hundreds of snake traps--funnel-shaped wire gadgets baited with live mice--set 30 paces apart at military facilities, including the sprawling Andersen Air Force Base. And each night, Hall goes on a snake roundup.

Among the most productive snake hangouts is a long chain-link fence at the edge of the limestone cliffs that tower over the hotels of Tumon Bay. On a warm spring night filled with blustery clouds dissolving into light rain, Hall cruises the fence in a pickup equipped with flashlights, heavy gloves and a fine mesh cage. Fellow snake-stalker Campbell rides on the hood. Ignoring the strains of disco music blaring from the hotels below, Campbell stares unblinking at the lengths of fencing as he drives past.

Inside the cab, Hall tells of the 2,500 or so snakes that he and his 10-man crew have captured and killed since his control effort went into full swing last September. He was hired in April, 1993, after federal studies--and Hawaii’s senators--persuaded territorial officials, who had dismissed biologists’ estimates as exaggerated, that something had to be done.

“This fence is a magnet for them,” says Hall, one hand on the wheel, the other aiming a spotlight out the window. “They follow the scent and dander left on it by birds and lizards. It doesn’t take long to find snakes here.”

“Whoa!” yells Campbell, leaping from the truck and sprinting toward a stick-like shape dangling from a strand of barbed wire. With one sweep of the hand, he yanks a two-foot-long snake off the wire, taking care to grasp the snake just behind its head.

The young snake wraps its strong prehensile tail around his wrist. “That bump in the middle of its body,” he says, “means it has a bird egg in its belly.”

In less than an hour, they nab seven more, several just a few hundred yards from a Continental Airlines jet and warehouse facility. “The closer we get to that warehouse, the more important each one of these snakes becomes,” Hall says, nodding toward a cage full of angry snakes writhing and striking at the mesh. “It’s a real battle.” Before the night is through, each snake will suffer what Hall calls a fatal cervical dislocation.

Rain or shine, the nightly raids along the fence at Tumon Bay and elsewhere will continue until scientists can devise a chemical attractant or some other bait to lure them into traps. Snake behavior expert David Chiszar is working on just such a potion at the University of Colorado at Boulder. There, in a high-security lab he calls “Merlin’s Cavern,” he studies 24 caged brown tree snakes that he brought from Guam under tight guidelines. The snake’s adaptability, Chiszar says, is impressive.

Most nocturnal tree snakes depend primarily on their acute night vision as they hunt. But this reptile easily switches to scent, enabling it to find prey in the undergrowth. It will even feed on carrion--unusual in the snake world.

“After extinguishing all the birds in certain areas on Guam, field researchers expected to see a decrease in the snake population,” Chiszar says. “Instead, they found it shifted its food source from birds to ground lizards.”

THE SNAKES’ MYSTERIOUS HABITS ARE OBSTACLE ENOUGH. BUT TERRITORIAL leaders have been slow to react with organized assaults. Those whose livelihood depends on Guam’s billion-dollar-a-year tourist industry point to the rarity of snake sightings as proof that the severity of the infestation has been exaggerated. Some even suggest that biologists have overstated the snakes’ numbers to ensure a steady stream of federal research dollars.

One doubter is Jim Tolan, who presides over what must be the most diverse complex of businesses on the island. In a three-story building, Tolan runs a lumber mill, a machine shop, an ammunition factory, a diesel parts store and a museum that houses a full-size jade chariot, a stuffed baby elephant, antique guns and Japanese erotic art.

“If we have such an abundance of snakes, where are the squashed snakes on the road? Do they look both ways before crossing the street?” asks Tolan, who has lived on Guam since 1956. “I think someone’s throwing some bull around. And because of that, it’s easier to find a reporter than a snake on this island.”

Local leaders say they have more important problems: coping with the typhoons that annually batter Guam; meeting the needs of the impoverished native Chamorus for better housing, education and jobs; and fighting for ownership of land now run by the military, which controls about a third of the island.

Guam’s governor, Joseph Ada, is extremely sensitive about the island’s image abroad, given that a third of the local jobs are fueled by tourists. Yet he is under pressure to work with federal wildlife authorities, which causes him to choose his words carefully.

On one hand, Ada says his administration is cooperating in efforts to eradicate the snakes. But during a lull in opening ceremonies for the recent 1994 Micronesia Games, he added, “The snakes aren’t that bad, they don’t bother us--they’re harmless.”

Then, a week later, as if on cue, the closing ceremonies for this gathering of track and field competitors from across the South Pacific were blacked out for an hour, courtesy of a brown tree snake that had slithered onto a power line. Since then, Ada has also had to call in Hall, the federal animal control officer. Brown tree snakes, it seemed, had been found roaming the grounds of the gubernatorial residence.