FYI on the brown treesnake

By Nate Hawley
Special to the Saipan Tribune

The brown treesnake (boiga irregularis) is a member of the Family Colubridae, which includes primarily harmless snakes. Generally 3-6 feet in length, the snake has been able to attain a length of over 10 feet. The snake is long and slender which facilitates its exceptional climbing ability and allows it to pass through tiny spaces in buildings where it rests during daylight hours. Snakes range from a lightly patterned brown to yellowish/green or even beige with red saddle-shaped blotches. The brown treesnake eats a variety of foods, including frogs, lizards, small mammals, birds and birds’ eggs.

ORIGIN OF THE SNAKE

The brown treesnake is native to coastal Australia, portions of Indonesia, New Guinea, and the Solomon Islands. It was most likely shipped to Guam as a stowaway in military cargo ships that moved materials after World War II. Upon arrival in Guam, the brown treesnake found a lot of prey and not many natural predators or diseases, allowing the snake to reach extremely high densities. Because it is so common on Guam, the snake it has been accidentally transported to other sites worldwide through civilian and military vessels and cargo. The snake now poses a significant threat to the biodiversity, economy, and human health within the Pacific region, including the Commonwealth of the Northern Mariana Islands, the State of Hawaii, the mainland of the United States and other sites regionally and internationally.

HUMAN HEALTH IMPACTS

The brown treesnake is a mildly venomous rear-fanged snake. When threatened, the brown treesnake is extremely aggressive and likely to lunge and bite. The bite frequently causes bleeding and local swelling and itching. Although no medically serious bites on adult humans have been recorded, the potential for serious incidents involving small children exists, especially with a large snake. The majority of the reported cases of snakebites on Guam occurred with small children. Snakebite is the cause of approximately 1 in 1200 emergency room visits on Guam. The snakes also seem to seek out small children and have been found on more than one occasion to select an infant when the child is sleeping between both parents.

ECOLOGICAL IMPACTS

Overall, the snake’s impact on Guam has been catastrophic ecologically. The brown treesnake is directly responsible for the extinction or local extermination of 9 of 13 native forests bird species and 3 of 12 native lizards. In the early to middle 1980s, certain native bird species were relatively common during standardized surveys of Northern Guam but declined dramatically over a one to three year period. The species of birds remaining on Guam occur only in special habitats where some protection from snakes exists. Even small mammals are extremely rare in most forested habitats of Guam. The brown treesnake is now considered the single greatest terrestrial ecological threat to the Commonwealth of the Northern Mariana Islands and is one of the greatest terrestrial ecological threats to Hawaii.

ECONOMIC IMPACTS

The brown treesnake is also responsible for frequent electrical power outages on Guam. Searching for prey near power sources and electrical lines, snakes simultaneously touch live and grounded conductors, which results in faults, short circuits, and electrical damages. This results in frequent losses of power to parts of Guam and even island-wide blackouts. Snakes have caused more than 1600 power outages in the 20-year period of 1978-1997 and most recently nearly 200 outages per year. Such power failures, brownouts and electrical surges damage electrical appliances and interrupt all activities dependent on electrical power including commerce, banking, air transportation and medical services. Costs to the island’s economy have exceeded $4.5M per year over a 7-year period without considering transformers, and damages inside electrical substations.

A University of Hawaii economic study recently estimated that the introduction of the brown treesnake to the State of Hawaii could cause between $28.5 and $405.1 million annually.

CONTROL AND CONTAINMENT EFFORTS

Since the brown treesnakes are not native to CNMI, the CNMI Department of Lands and Natural Resources (DLNR), with the help of federal agencies, currently monitor all CNMI ports of entry and other high-risk areas. Approximately 300 brown treesnake traps have been strategically placed around high-risk areas to prevent the snake from establishing itself. The CNMI-DLNR also utilizes five detector dog teams that inspect high-risk cargo originating in Guam. The government also erected a containment barrier at Saipan’s commercial seaport to be utilized as a brown treesnake quarantine facility for high-risk cargo.

Brown treesnake awareness and outreach is crucial in preventing the spread of this invasive pest. Media statements and public demonstrations by CNMI-DLNR stress the importance of reporting all snakes to officials immediately.

SNAKE SIGHTINGS IN THE CNMI

THERE ARE NO NATIVE SNAKES IN THE CNMI, THEREFORE ALL SNAKES SIGHTED SHOULD BE REPORTED IMMEDIATELY TO DIVISION OF FISH AND WILDLIFE STAFF TO THE 24HR HOTLINE, 28-SNAKE (287-6253)

There have been a total of 103+ brown treesnake sightings reported in the CNMI since 1982. Sixty-nine of the sightings are considered credible brown treesnake sightings, with 13 documented captures.

Island Breakdown:
Rota: 2 credible BTS sightings resulting in 2 BTS captures
Tinian: 5 credible sightings resulting in 0 BTS captures
Saipan: 62 credible BTS sightings resulting in 11 BTS captures
CNMI Total : 69 credible BTS sightings, 13 BTS captures

There is a general agreement between brown treesnake experts that there are brown treesnakes on Saipan, but it is not clear if they are breeding or self-sustaining. There have been no pregnant females or juvenile snakes captured in the CNMI thus far but this pattern was true on Guam previously.

REPORT SNAKE SIGHTINGS

Any snake sighted/captured in the CNMI should be reported IMMEDIATELY to 28-SNAKE (287-6253). To dramatically increase the probability of a capture, every effort should be made to maintain sight of the snake until DLNR staff arrive at the scene. If a dead snake is found, it should be placed in a plastic bag and frozen it until it can be transferred to a local biologist or government agency. Snakes sighted in the greater Pacific region may also be reported to the Pacific Region BTS Hotline at 671-777-4477 (671-777-HISS).

(Hawley is the herpetologist at the Division of Fish and Wildlife.)