The pupils at Waitahuna School, South Otago, asks :-

Occasionally after heavy rain we get a huge amount of these worms outside our class. We had yesterday off school as the flooding of the Waitahuna River was quite serious and we came back to these visitors. What are they?

Trish Fraser, a soil scientist with Plant and Food Research, responded.

From the photograph and video that you supplied, it appears that you have found a rather large gathering of “enchytraeids�.

These creatures are also more commonly known as ‘potworms’. They are widely distributed from the tropics to the polar regions and are a group of small to medium sized earthworm-like animals (Phylum Annelida and in the Class Oligochaeta). They are effectively like smaller cousins of earthworms and they carry out similar jobs to earthworms in the environment. Their ‘family’ is known as Enchytraeidae which includes nearly 700 different species, most of which live on the land, but there are some aquatic (water-loving) species too. They tend to live in soil, compost, mosses, decayed wood, sands near the seashore and can also be found in fine sediments in the deep sea.

Although some species of enchytraeids are specialised, and like to live in glacier ice and snow, in general most species of enchytraeids like to live in sites where there is a lot of organic matter present. So people sometimes notice them in compost heaps as this is a place with large amounts of organic matter (dead and decaying plant material). Lots of enchytraeids like to grow where things have been added that make compost more acidic, as they appear to particularly enjoy that kind of environment.

In some soil environments you can even find over 300 000 individuals in just a square metre! This partly explains why you found so many at your school as they may have been washed out of the soil when the flood came and then gathered together for protection.

Enchytraeids usually live in the top five to ten centimetres depth of soil and they play a very important role in helping to decompose or break down things like dead and decaying plant material in the soil, making the nutrients contained in that dead material into a form that will be once again available for plants to take up (this is known as nutrient cycling).

Although identification of individual enchytraeids has been very difficult in the past, scientists now have new tools becoming available to them that are making it a lot easier to identify them. As a result, as has previously been done for earthworms, it has been recently suggested that we could now even consider using enchytraeids as good biological indicators of changes in land use and management. In this way scientists can investigate how humans are affecting or changing the land beneath us by measuring changes in the soil biota (includes creatures such as earthworms and enchytraeids).

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