Current Invasive Species Crisis

Scientific name: Boiga irregularis

Introduced: Late 1940s–early 1950s

The brown tree snake is Guam’s most notorious invader. Accidentally introduced via military cargo after World War II, it has driven 10 of the island’s 12 native forest bird species to extinction and decimated populations of lizards and small mammals. The snake also causes frequent electrical outages, costing millions in damages each year.

Primary impacts:

• Elimination of most native forest birds and drastic reduction of pollinators and seed dispersers.
• $1–4 million in annual power outage damages and expensive control efforts.
• Threat to pets, poultry and human safety; hundreds of snake bites treated annually.

Quick facts:

• Peak densities of up to 29 snakes per acre—among the highest ever recorded.
• Estimated 30–50 snakes per hectare remain on the island.
• Management costs exceed $7 million per year.

Scientific name: Oryctes rhinoceros (CRB‑G biotype)

Introduced: 2007

This large beetle bores into the crowns of coconut palms and pandanus trees, causing tree death and threatening to eliminate Guam’s iconic palms. Detected in 2007, the CRB‑G biotype resists traditional biological control agents and has spread across the island.

Primary impacts:

• Destroys coconut palms and culturally important pandanus trees.
• Reduces food sources for coconut crabs and native wildlife.
• Millions spent on failed eradication efforts and ongoing management.

Quick facts:

• First detected near Tumon Bay in September 2007.
• Typhoon Dolphin in 2015 triggered a population explosion.
• Biotype CRB‑G is resistant to the OrNV virus used elsewhere as biocontrol.

Scientific name: Aulacaspis yasumatsui

Introduced: 2003

The tiny cycad aulacaspis scale insect has devastated Guam’s native cycads. Since its introduction, it has killed more than 90 percent of Cycas micronesica plants, including century‑old specimens. Surviving plants suffer stunted growth and poor reproduction.

Primary impacts:

• Near‑total loss of culturally significant cycads.
• Loss of habitat for pollinator moths and other associated species.
• Legacy effects on forest regeneration and soil stability.

Quick facts:

• Guarantees plant death within one year of infestation.
• Cycas micronesica listed as endangered in 2015.
• Biocontrol programmes are underway but funding is limited.

Scientific name: Wasmannia auropunctata

Introduced: 2011

The little fire ant, sometimes called the electric ant, forms supercolonies that blanket the ground and trees. Its painful sting affects people, pets and wildlife, making outdoor activities uncomfortable and threatening agriculture.

Primary impacts:

• Threatens native insects, lizards and birds through predation and competition.
• Stings cause dermatitis and can blind animals, including pets.
• Hitchhikes in green waste and cargo, raising the risk of spread to other islands.

Quick facts:

• First discovered at a landfill in northern Guam in 2011.
• Approximately 11 established sites across the island.
• Control efforts focus on early detection and targeted baiting.

Species: Philippine deer (Rusa marianna), feral pigs (Sus scrofa), water buffalo (Bubalus bubalis)

Introduced: 1600s–1770s

These hoofed mammals were introduced centuries ago for food and draft power. Today their growing populations trample native vegetation, cause erosion, foul waterways and facilitate the spread of invasive plants and diseases.

Primary impacts:

• Damage to forest regeneration through grazing, rooting and trampling.
• Increased soil erosion and sedimentation of rivers and reefs.
• Contamination of water supplies with E. coli and other pathogens.

Quick facts:

• All three species are culturally significant but ecologically destructive.
• Populations fluctuate with hunting pressure and storm events.
• Management includes fencing, selective culling and community outreach.