Yes, there are snakes in Guam, but the situation is dominated by a single, highly invasive species, the Brown Tree Snake (Boiga irregularis). This prolific predator has fundamentally reshaped the island’s ecosystem, leading to an environmental crisis. The story of snakes in Guam is the story of a single species that has radically altered the balance of nature in a relatively short period.
The Brown Tree Snake Invasion
The Brown Tree Snake (BTS) is native to parts of eastern Indonesia, Papua New Guinea, and coastal Australia. It arrived in Guam accidentally shortly after World War II, likely transported as a stowaway in cargo shipments, particularly on U.S. military vessels. Detected near the naval port facility in the 1950s, the snake’s population boomed across the island due to the absence of natural predators.
The snake’s physical and behavioral traits made it a successful colonizer. It is a slender, arboreal, and highly agile snake that typically ranges from three to six feet, though it can grow up to 10 feet. The BTS is a nocturnal, rear-fanged colubrid, possessing a mild venom delivered through grooved teeth. While not dangerous to adult humans, its climbing habit posed a significant problem for native species that lacked defenses.
The Ecological Crisis Caused by the Snake
The introduction of the Brown Tree Snake created an ecological disaster by decimating Guam’s native bird and bat populations, which had evolved in a snake-free environment. Ten of the island’s 12 native forest bird species were extirpated from Guam, including the Guam Rail and the Guam Flycatcher. The absence of natural defenses made the birds and their eggs easy prey for the efficient, tree-climbing snakes.
The impact cascaded beyond the immediate loss of birds, affecting the fundamental structure of the island’s forests. With native birds gone, the crucial ecosystem service of seed dispersal was severely disrupted, as 60 to 70 percent of native tree species rely on birds for this function. This loss has led to a significant reduction in native tree seedlings, threatening the long-term viability of the forest canopy. Furthermore, native lizard populations have also declined, with some species reduced by up to 40 percent.
Beyond the biological realm, the snakes have caused extensive damage to Guam’s infrastructure. Due to their arboreal nature and ability to climb, they frequently slither onto power lines and into electrical substations. The resulting short circuits cause frequent power outages, which historically occurred as often as every other day, costing the island millions of dollars annually. The economic and ecological damage has made the Brown Tree Snake a global example of a devastating invasive species.
Ongoing Efforts to Control the Population
Controlling the massive Brown Tree Snake population, estimated to be in the millions, requires unconventional and highly coordinated methods involving U.S. agencies like the Department of Agriculture (USDA) and the Department of Defense (DoD). One unique control technique involves the aerial deployment of dead neonatal mice laced with 80 milligrams of acetaminophen, the active ingredient in Tylenol. Acetaminophen is safe for humans but is lethally toxic to the Brown Tree Snake, causing fatal hypoxia.
The poisoned mice are attached to small cardboard parachutes designed to snag in the tree canopy, placing the bait directly where the arboreal snakes hunt. This method exploits the snake’s scavenging behavior and minimizes the risk to non-target species on the ground. Simultaneously, biosurveillance programs are run at airports and seaports to prevent the snake’s spread to other vulnerable Pacific islands, such as Hawaii and Saipan. These efforts, which also include conventional trapping and barrier installation, represent a long-term management strategy aimed at population suppression rather than complete eradication.
Other Reptiles and Non-Native Species
The snake population on Guam is almost entirely composed of the invasive Brown Tree Snake, as the island had virtually no native snake species prior to its arrival. The only other snake encountered is the non-native Brahminy Blind Snake (Ramphotyphlops braminus), a tiny, harmless, burrowing species often mistaken for an earthworm. The Brown Tree Snake is Guam’s singular snake concern, primarily posing an ecological and infrastructure problem.
While other non-native reptiles, such as geckos and monitor lizards, exist on the island, they do not pose the same systemic threat as the BTS. The Brown Tree Snake is mildly venomous but is not considered a physical danger to adult humans. The threat it presents is to the island’s ecological integrity and its electrical power grid.