Pomacea diffusa

Apple Snails (Pomacea spp.) are freshwater snails commonly sold in the aquarium trade for the purpose of keeping aquarium glass clean of algae. However, if released, these snails, native to South America, are a potentially serious biological threat to the waterways of Australia. The most destructive species is the Golden Apple Snail, Pomacea canaliculata, a voracious vegetarian which has decimated the rice fields of eastern Asia.

Another closely allied species is the Spike-top Apple Snail, Pomacea diffusa (previously classified as P. bridgesii). This is a detrital feeder, and although not a threat to vegetation, could have serious ecological ramifications, displacing native freshwater snails if established here in the wild. In December 2006, a significant population of the Spike-top Apple Snail was discovered in a waterway on the north side of Brisbane. Since then other occurrences of this invasive species have been recorded to the east, south and west of the city.

The Spike-top Apple Snail's most obvious features are 'square shoulders' at the tops of the whorls, a very large, oval aperture and a deep umbilicus. It has a high, somewhat pointed spire which gives rise to the common name term 'spike-top'. Mature apple snails can grow as large as a golf ball or sometimes larger. The shell may be 40-70 mm high and 40-50 mm wide, and colour varies from yellow to greenish brown, some forms having dark spiral bands. The yellow form was originally bred in Florida, USA and these variations are often referred to in the aquarium trade as 'mystery snails'. The snails leave the water to lay their eggs. In an aquarium, they climb the side of the tank and deposit over 100 pink-coloured eggs that hatch in two to three weeks.

The Golden Apple Snail, a similar species, would be truly hazardous if released into the Australian environment. This pest has a broad appetite for water plants and could be expected to have dramatic effects on aquatic vegetation and native freshwater fauna throughout much of eastern Australia. In many Asian countries, toxic pesticides have been added to waterways in vain attempts to eradicate or control the species. This practice would be out of the question with regard to Australia’s rivers and lakes, and mechanical methods of control have proved highly expensive and ineffective elsewhere.