April 2018

Wandering worm

Is this the scourge of the Wet Tropics, the introduced Brazilian earthworm Pontoscolex corerthrurus?

Answer

A native megascolecid earthworm. Introduced Pontoscolex corethrurus found in a Brisbane garden. Pontoscolex corethrurus, showing diagnostic pink spots.

The earthworm in the photo is a native species and is a member of the family Megascolecidae; it probably belongs to one of the pheretimoid genera within this family. In this case, identification to species is not possible from a photo. Earthworm identification can be difficult and almost always requires either dissection of the specimen or DNA analysis.

Australia has more than 350 native species of earthworms, and more remain to be discovered. Particularly famous is the Giant Gippsland Earthworm (Megascolides australis), which can grow to at least four metres long. Other spectacular, if somewhat smaller species include the Giant Earthworm (Digaster longmani) which may reach two metres and the Queensland Turquoise Earthworm (Terriswalkerius terraereginae) which can reach 60cm in length and the thickness of a human thumb.

The introduced species of concern is Pontoscolex corethrurus. It can be identified by a distinctive pattern of three pink spots visible through its skin (see image). Pontoscolex corethrurus is thought to have originated in the north-east of South America, but has now spread into humid tropical habitats around the world. They seem to have been accidentally introduced by humans; soil-living animals can be easily spread in soils and potted plants. Like many invasive species, it is most common in disturbed habitats (those altered by human activity). Pontoscolex corethrurus is found in far north Queensland and south-east Queensland. Museum records indicate that it has been present in Cooktown since at least the 1890s (Museum of Victoria collection) and since then has probably spread throughout the Wet Tropics.

Earthworms are important ecosystem engineers, capable of altering the composition and structure of soils. They do this by feeding on organic matter (thus returning nutrients to the soil), burrowing through the soil (allowing air, water and plant roots to penetrate the soil), and even spreading nitrogen-fixing bacteria (increasing soil nutrients).

While numerous species of earthworms have been introduced to Australia (almost 20% of species in Queensland are introduced), the effects that they’ve had on the environment and local species are hard to measure.

Some evidence from overseas studies suggests that P. corethrurus doesn’t compete with native species (it occupies a new habitat: disturbed areas). However, Queensland Museum records indicate that it occurs in various habitats throughout the Wet Tropics, so it may potentially compete with native species.

You can read about the many different types of animals that are collectively referred to as ‘worms’ on this factsheet (426 KB) pdf document icon.

Earthworms have featured on Question of the Month before

 


 


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