Invasives / Pests

Rattus rattus

Accidentally introduced via ships, pose threats to seabird colonies and native plants. 

Mus musculus

Accidentally introduced via ships, pose threats to seabird colonies and native plants.

Oryctolagus cuniculus

Introduced at an unknown point in the past perhaps from domestic pets. Rabbit numbers were high up until an illness wiped out the majority of the population in 2024.

No ants are native to Ascension. All species present today were accidentally introduced by people, mainly through shipping and cargo. Several species are now widespread, especially around settlements and disturbed areas. Some, such as the invasive big-headed ant (Pheidole megacephala), can form large colonies and disrupt native invertebrates and ground-nesting seabirds. Despite their small size, ants have had a significant ecological impact on the island.

Several species are present, including the southern house mosquito (Culex quinquefasciatus), which is the most widespread. Mosquitoes breed in standing water, such as cisterns, tanks, and puddles, and are a nuisance to both people and wildlife. 

All cockroaches on Ascension are introduced species, brought in accidentally with ships and cargo. Several kinds are now well established, particularly around human settlements and buildings. The American cockroach (Periplaneta americana) is the most common, often seen in warm, damp places.

Acridotheres tristis

The common mynah was introduced to Ascension in the 19th century to control pests such as ticks. Since then, it has spread widely across the island and become one of the most familiar birds in settlements. However, mynahs are aggressive and adaptable, competing with native species for food and nesting space. They also damage crops, spread invasive plants by dispersing seeds.

Prosopis juliflora

Mexican Thorn was introduced to Ascension in the 1960s. It has since become highly invasive, spreading across wide areas of the island. The dense thickets it forms outcompete native plants, restrict access for people and wildlife, and alter habitats. Its long spines can injure animals and damage tyres, making it a nuisance as well as an ecological threat.

Psidium guajava

Guava was introduced to Ascension as a fruit tree and remains common on the island. While valued for its edible fruit, guava has spread into the wild and can form dense thickets, especially in moist areas such as Green Mountain. It outcompetes native vegetation and alters habitat structure, making guava one of Ascension’s invasive plant species.