New Zealand has over 200 known species of earthworms, with new species being identified as they are discovered. Of these, the majority are both native and endemic, meaning they are found in New Zealand and nowhere else. However, the earthworms we are most likely to encounter on rainy footpaths or in garden soil are introduced species.
Acanthodrilidae, Octochaetidae, Megascolecidae (mostly New Zealand native species)
Lumbricidae, Glossoscolecidae (all introduced species)
Earthworms have been in New Zealand for a very long time. It is possible they were among the first animals to colonise the land but they are very slow to evolve. Scientists think earthworms came to New Zealand in two waves. The Acanthodrilidae family most likely arrived in the Cretaceous period (65–145 million years ago). This group of earthworms is almost entirely endemic, meaning they have been in New Zealand long enough to evolve into species not found anywhere else in the world. The Megascolecidae family probably arrived in the Tertiary period (1.8 million–65 million years ago). Although native, they are not endemic, meaning these species exist in other parts of the world.
Native earthworms were once widely distributed throughout New Zealand. They became highly specialised to live in particular types of forests, resulting in many different species. Most species have been unable to adapt when their forest homes have been converted into agricultural land such as pasture, and they have not survived in pastoral soils. Many native species are now confined to indigenous forests or areas where the soil is largely undisturbed. We don’t know a lot about some of our native earthworms. Their life cycles, distribution ranges and environmental requirements are not well known. Some of this is due to the remoteness of forest habitats. The Department of Conservation lists about 170 native species of earthworm as threatened or endangered, partly because so little is know about them.
Native earthworms range in size from the smallest, Diporochaeta punctata – a tiny leaf mould dweller less than 2 centimetres long – to the largest, Spenceriella gigantea – a subsoil earthworm that can grow up to nearly 1.5 metres in length! Some of these native species were prized by pre-European Māori for their usefulness either as bait or as a food source. Noke waiū is a large, milky white earthworm found in the forest. It was threaded onto flax and looped to make an eel bob. The worms act as bait while the flax acts as a snare, becoming entangled in the eels’ teeth. Transactions published by the Royal Society New Zealand in 1902 mention whiti and kurekure earthworms as food reserved for the chiefs because their sweet flavour was said to remain in the mouth for 2 days. Earthworm delicacies still feature in wild food festivals today.
As far as is known, all of the species belonging to the Lumbricidae family arrived in New Zealand by accident. The earthworms arrived in a number of ways. For example, as European settlers brought plants into the country, earthworms or their cocoons were amongst the roots or in the soil. Soil was also used as ships’ ballast. It was offloaded at ports when no longer required, and the earthworms began to spread out on their own accord. After noticing the pastoral improvement in areas where the lumbricid earthworms were present, some farmers began to deliberately introduce them to their land.
This is one instance where introduced species have had a positive effect in the New Zealand environment! Native earthworms do not generally live in cultivated soils so there is no competition or threat from introduced species in agricultural soils. The lumbricid species are the most common earthworms found in New Zealand, but their distribution is patchy. Scientists such as Dr Nicole Schon are trying to quantify the potential benefits of large-scale introductions of anecic lumbricid earthworms to pasture soils. They maintain permanent burrows that increase soil porosity and water infiltration. In addition, they incorporate organic matter deep into their burrows, potentially improving carbon storage in soil. This benefits the soil and may be a way to offset carbon dioxide (greenhouse gas) emissions.
Nature of science
Funding influences the direction of scientific research. Introduced earthworms have direct benefits to agriculture – New Zealand’s largest export earner. Research into their habits and behaviours is therefore more likely to be funded. As native earthworms are not currently thought to be economically important, there is little funded research about them being carried out.
Read how some boys in the 1920s used earthworms to make eel bobs.
It is thought that New Zealand native earthworms came from the Indo-Malayan or Australian regions and entered New Zealand across a land connection from the north. View this animated video to see how the New Zealand landmass split from Gondwana.