Potential Threats to the Tiwi Islands

Strict biosecurity protocols are in place on the Tiwi Islands however, the high volume and frequency of freight movement from the mainland to the islands means the risk of weed and pest incursion still exists. Tropical fire ants and cane toads are not on the Tiwi Islands but post a significant threat. Please report any potential sightings immediately to the Tiwi Rangers.

Tropical Fire Ants

Tropical fire ants (Solenopsis geminata) were present on Melville Island for more than 20 years but were eradicated in 2025. Their aggressive nature, painful venom and ability to form large colonies make them a significant threat to human health, ecosystems, native wildlife and agriculture. Stings can trigger severe, life-threatening allergic reactions like anaphylaxis.

Although the Tiwi Islands are free of Tropical fire ants and biosecurity protocols have improved, there is an ongoing risk of reintroduction.

Tropical fire ant identification

Tropical fire ants are small (2-4 mm), slow moving, and yellow/orange in colour. The ant gets its name from the painful burning feeling produced by its powerful sting. It is closely related to the Red imported fire ant (Solenopsis invicta) found in eastern Australia.

Worker ants come in many sizes, with the largest being at least five times the size of the smallest and having very large heads. Nests are very conspicuous, with freshly worked earth heaped into a pile, particularly on patches of lawn or in pot plants. Semi-subterranean trails up to ten metres or more long are also a common sight extending from the colonies, particularly after rain. The ant is rarely found inside houses.

Cane Toads

Cane toads (Bufo marinus) became pests after being introduced into Australia in the 1930s to control destructive beetles in Queensland’s sugarcane crops. Cane toads are poisonous during all life stages and predation of the invasive species by native wildlife is a significant risk to biodiversity. Population declines of more than 80 per cent in some species, such as goannas and freshwater crocodiles, can occur due to lethal poisoning when predators attempt to eat toads.

Cane toads arrived in Darwin in 2005 and by 2011 were established in the Kimberley in Western Australia. They are currently not found on the Tiwi Islands.

Cane toad identification

Adult cane toads are large, generally 9-15 cm long, but can grow up to 24 cm. They are heavily built and the skin on top is rough, dry and covered in warts. The colour can vary from grey, olive, yellow-brown to red-brown. Their underparts are lighter and usually a mottled brown.

Cane toads have an upright stance and walk or move small distances in short, rapid hops, unlike most native species, which leap. They are unable to jump high and are poor climbers. They also need daily access to water.

Male toads have a distinctive call, a high-pitched broken brrrr sound, similar to a motor running or a long loud purring trill.

Cane toad eggs are laid in long chains with individual eggs which look like black beads encased in jelly. Often eggs are in double rows along the strand. Tadpoles are shiny black on top and have a plain dark bluish grey or black belly. They do not come up to the surface to breathe like the tadpoles of native frogs.