Species Profiles

The brown tree snake (Boiga irregularis) is a nocturnal arboreal serpent native to Australia, Papua New Guinea and the Solomon Islands. It was accidentally introduced to Guam shortly after World War II, likely in military cargo. Without natural predators, its population exploded. The snake feeds on birds, lizards, small mammals and even poultry, leading to the extinction of 10 of Guam’s 12 native forest bird species.

In addition to devastating wildlife, the snakes climb power poles and transformers, causing frequent electrical outages. One study found that brown tree snake–caused outages cost Guam’s economy about $4 million in lost productivity each year.

Introduced	Late 1940s–early 1950s
Size	Up to 3 m long; slender body with large head
Diet	Birds, lizards, bats, small mammals
Threats to Guam	Caused native bird extinctions and power outages; bites pets and people

The coconut rhinoceros beetle (Oryctes rhinoceros) is a large scarab beetle whose larvae develop in rotting vegetation. Adults bore into the crowns of coconut palms and other trees, killing them. The CRB‑G biotype, detected near Tumon Bay in 2007, is resistant to the virus that has been used for biocontrol in other regions. According to the Guam Department of Agriculture, at least 25 percent of the island’s coconut trees have already been damaged by this beetle.

This pest threatens not just iconic palms but also pandanus trees, which are culturally important for weaving and traditional crafts. Its spread has been aided by typhoons and the movement of green waste. Farmers and foresters spend millions on surveillance, sanitation and tree removal programmes.

Introduced	2007
Size	Adults up to 6 cm long with characteristic horn
Diet	Feeds on sap and decaying plant material; adults bore into palm crowns
Threats to Guam	Destroys coconut and pandanus trees; reduces food and habitat for native species

The Asian cycad scale (Aulacaspis yasumatsui) is a tiny sap‑sucking insect that infests the leaves, stems and roots of cycads. First detected on Guam in 2003, it quickly spread and killed more than 90 percent of wild Cycas micronesica plants. The scale protects itself under waxy armor and hides in plant crevices, making control difficult.

This insect disrupts photosynthesis and nutrient flow, causing yellowing leaves, stunted growth and eventual death. Biocontrol programmes using predatory beetles have shown some success but require continuous monitoring and funding.

Introduced	2003
Size	Less than 2 mm; white scale covers plant surfaces
Diet	Feeds on plant sap, sucking nutrients from cycads
Threats to Guam	Causes near‑total loss of native cycads and associated species

The little fire ant (Wasmannia auropunctata) is a tiny, slow‑moving species that forms dense supercolonies. Its painful sting and tendency to forage in trees as well as on the ground make it a menace to people, pets and wildlife. Experts rank it among the world’s worst invasive species; it monopolises resources and displaces native insects, lizards and birds.

Repeated stings can cause blindness in livestock and companion animals, and severe allergic reactions, including anaphylactic shock, in humans. These ants hitchhike in potted plants, green waste and cargo, raising the risk of spread to other islands and undermining tourism and outdoor recreation.

Introduced	2011
Size	Workers only 1.5 mm long; pale orange‑brown
Diet	Honeydew from sap‑feeding insects, seeds, small arthropods
Threats to Guam	Injures people and animals; displaces native species; spreads easily

Feral ungulates on Guam include Philippine deer (Rusa marianna), feral pigs (Sus scrofa) and water buffalo (Bubalus bubalis). These mammals were introduced between the 17th and 18th centuries for food and transport. Lacking predators and benefiting from hunting bans near urban areas, their populations have increased. They eat seedlings and understory plants, trample soil and spread invasive seeds, hampering forest regeneration.

Research has shown that while pigs may help disperse some seeds in the absence of birds, deer have a negative impact on seedling survival and forest recovery. Combined with rooting and wallowing behaviour, these ungulates accelerate erosion and degrade water quality.

Introduced	1600s–1770s
Size	Deer 25–60 kg, pigs 50–90 kg, buffalo up to 300 kg
Diet	Herbivorous; eat seedlings, roots, fruits and crops
Threats to Guam	Destroy vegetation, erode soil, damage crops and spread pathogens