An Invasion of Guam

An Invasion of Guam

In June 1944 a platoon of U.S. infantry soldiers was on combat patrol in Dutch New Guinea (now West Irian). As they pushed through dense underbrush one of the soldiers reached up to balance himself by grabbing a low—hanging branch. This could have been a fatal move. The branch was already occupied by a five—foot brown snake that promptly bit him on the thumb. The two soldiers standing behind him immediately reacted by attacking the snake with unsheathed bayonets and hacking it into oblivion. They dared not fire their rifles because the enemy would certainly hear the shots and set up an ambush.

The bitten soldier sank to his knees, his face ashen with fear. The platoon medic hurried to the scene; he was a medical doctor who by coincidence knew something about snakes. He examined the remains of the brown snake and eased the victim's mind by identifying it as a species of Boiga that was only mildly poisonous. Apparently he was right, for the soldier was sent to a rear base hospital for only a few days and released back to duty.

Specimens of this variety of snake have continued to bite creatures, including people, not only in New Guinea but also on the island of Guam. Properly identified as a tree snake, Boiga irregularis is a natural inhabitant of New Guinea and Australia. So what the heck is it doing on Guam, over 1,200 miles to the north?

Guam is the largest and southernmost of the Mariana Islands in the west central Pacific. An unincorporated territory of the United States and an important military base, the island is only 30 miles long and from 4 to 8 miles wide. With a total area of about 209 square miles, Guam is smaller than Molokai, fifth in size of the eight Hawaiian Islands. Bats, rodents, lizards, and several birds are the principal native animals, but deer and wild pigs have been introduced. Into this island paradise came the brown tree snake, Boiga irregularis.

A rear—fanged snake of the subfamily Borginae, the brown tree snake has a couple of enlarged teeth in the back of the upper jaw that are grooved from top to bottom. The teeth underlie the poison gland so that, when the snake bites, the gland secretes a mild venom that trickles down the tooth grooves into the victim's wound. The snake is up to 10 feet long, but it has a relatively small head, so the mouth doesn't open wide enough to get a good grip on its victim. This, along with the mild venom, may explain why there have been no human casualties even though a number of residents have been bitten.

The snake appears to be mainly nocturnal, although many are seen during the day. B. irregularis climbs trees with great speed, and it is also quite agile on the ground, where it almost always seems to travel in a straight line. It invariably seeks to reach the nearest high point, be it a tree or telephone pole, and its main prey is definitely birds!

Prior to the 1950s, Guam had six endemic species of birds (they existed nowhere else in the world) and several species of native, nonendemic, birds. Almost all are now extinct on Guam, along with three species of bats and a variety of lizards. The decline of birds was first noticed in 1978, but its cause was not identified until several years later, and the situation continued to worsen daily.

About 1952, a military cargo plane landed in Guam after a brief stop in New Guinea. The supplies were unloaded, along with an unobtrusive stowaway, a pregnant Boiga irregularis. With no apparent threats in her new home, she produced her brood in safety. To the brown tree snake this was a veritable Garden of Eden. With little competition and no natural enemies, B. irregularis multiplied completely out of control. In less than 40 years the snake population that began with a single pregnant female has exploded to an estimated one million to three million. This averages out to about 10,000 snakes for each of Guam's 209 square miles! Since snakes don't space themselves evenly, their density in one particular area was calculated in 1992 at 30,000 per square mile. That would amount to 62 snakes per football field heading for the goalposts and light poles and hundreds of others in bleachers, press boxes, and control booths.

In 1982 concerned citizens of Guam brought in a biologist to find what was causing the decline in their bird population. Eventually the biologist turned her attention to the rather plentiful snake that natives called the Philippine rat snake. The first one she cut open had birds and eggs in its digestive tract. She offered a bounty for each "Philippine rat snake," and virtually every one of the throngs of snakes brought to her laboratory showed remains of birds and eggs. The culprit was B. irregularis, which continued to multiply as the birds declined.

Before the brown tree snake arrived from New Guinea, Guam had been almost as snakeless as Ireland. The only native serpent was a burrowing blind snake that looked like a worm and fed on termites. The birds of Guam evolved in the absence of snake predators, so they were naive, incautious, and totally defenseless in the face of an enemy. B. irregularis, having left its enemies behind, faced a bountiful food supply on a utopian island, but only until it completes the job of exterminating all edible animal life. Most of the surviving birds of the remaining endemic species have been taken from Guam to zoos on the U.S. mainland. The goal is to breed them back into populations large enough to be released back on Guam; in the meantime B. irregularis must be controlled or eliminated from the island.

At present, people who go for a nature walk or drive on Guam see snakes draped over power lines, telephone poles, and just about every tree around. Electrical power outages are common as snakes slither into power boxes and cause short circuits. People have become accustomed to being plunged into darkness; over 50 outages a year occurred during the 1980s. But herein may be a partial solution to the overabundance of B. irregularis.

Recently two repairmen investigating an electrical short circuit found, not to their surprise, a well—toasted Boiga coiled around the power box. They took it home and, with a courage based on "don't knock it till you've tried it," sampled some of the fried snake. They were amazed to find that it tasted like well—seasoned chicken, and it proved to be quite digestible. The word spread about the reptilian chicken, and others who dined on this inexpensive substitute found it entirely acceptable. Perhaps the brown tree snake has finally met its predatory match, and humans will be able to partially undo what they were inadvertently but carelessly responsible for doing. If Guamanians serve enough snakeburgers in place of hamburgers, the ecological system of the island may self—correct. Then, for the remaining birds, bats, and lizards, paradise may be regained.

However, it is most unlikely that human predation will keep up with the population explosion of B. irregularis, so wildlife specialists on Guam are advising folks to learn to live with snakes. This includes accepting their invading homes, even attacking infants, and being a part of all outdoor activities. Unfortunately, their original invasion was so easily accomplished that it could be repeated. The brown tree snake, Boiga irregularis, has been found on aircraft that have arrived on Hawaii from Guam. Another paradise lost?

From the book: 
Petrified Lightning