The legacy of Smaug: Exotic worms conquer New Zealand’s soils

My armour is like tenfold shields, my teeth are swords, my claws spears, the shock of my tail is a thunderbolt, my wings a hurricane, and my breath death!” Smaug from The Hobbit, by JRR Tolkien.

Wyrms or worms? It’s probably not the introduction you’d expect from your typical friendly neighbourhood earthworm, but as it turns out, they’re not as harmless as they may seem. Could it be that introduced specimens are actually taking over the home-soils of worms native to Aotearoa New Zealand?

I am king under the mountain!
Image by whadatobexy (CC)

An invasion as ruthless as that of Smaug (you know, the “specially greedy, strong and wicked worm” described in JRR Tolkiens “The Hobbit”), when he drives the dwarves from their tunnels beneath the Lonely Mountain? Well, maybe.

New Zealand is actually one of the countries with the highest number of endemic earthworms (“endemic” meaning they exist nowhere else in the world). It has over 200 different species, all of them in the Megascolescidae family.

They thrive in soils of native vegetation but rarely survive in land used for agricultural purposes. For this reason, it’s fair to assume that the land-use-change, caused first by the Māori, then the Europeans, was not appreciated by the worms living in that ground. With the introduction of agriculture and pastures, it didn’t take long for native earthworms to disappear, only hanging on in areas that were still covered with the original vegetation.

Twenty-three species of European earthworms (from the Lumbricidae family) were introduced. They quickly took over the changed habitats and ecological functions from their New Zealand worm-cousins, which themselves continued to live in exile, deep within the realms of untouched soils (this, and further information can be found here).

As described here, European species have been moving from agricultural land into adjacent native vegetation. We know from other parts of the world, like the US, that the presence of invading exotic earthworms causes changes in the soil, such as nutrient levels. This has effects on the entire ecosystem as well as on the native worms living there.

One of the first studies to look at the co-existence of the exotic and native earthworm species in New Zealand was done by researchers from Lincoln University in 2016. The study was called “Response of endemic and exotic earthworm communities to ecological restoration“. The goal of the project was to find out if endemic earthworm species would come back to recolonise areas where native vegetation has been restored. The study looked at  two sites, located on the east and on the west coasts of New Zealand’s South Island. On one of them, plant restoration had been happening for over 30 years, on the other for 8 years.

The team of researchers excavated soil from each site and hand-sorted out all worms present. In the lab, they were carefully identified as either endemic or exotic. After the slimy work was done, the following conclusion was reached: the populations of endemic worms increases alongside the length of the restoration period. In the meantime, the population of exotics remained more or less stable.

In restored sites exotic and endemic earthworms can co-exist in native soil. However, exotics may make life more difficult for New Zealand’s endemic worms, perhaps by making the soil less favourable for them, or just eating up the yummy leaf-debris. Further studies are urgently needed! However, despite these negative implications, are exotic earthworms just another invasive species in New Zealand, something we should get rid of to save the natives?

The endemic worms are definitely not as feisty as JRR Tolkiens dwarves (I imagine them perhaps with more of a sedate and gentle character, more hobbit-like really, lots of second breakfasts and idling around the Shire). They most likely aren’t planning a revolt to reconquer their homeland that has been turned into pastures and cropland.

Today, agriculture plays an immense role in New Zealand, and the European worms have become indispensable to the farmland areas, as as they provide many benefits in terms of waste recycling, soil fertility and crop productivity. This has encouraged efforts to continue increasing the dispersion of exotic earthworms in New Zealand’s agricultural land in recent years. It seems the exotic worms, like Smaug, are already hoarding the “gold” of the New Zealand’s fertile lowland agricultural soils and have begun expanding their sovereignty into the depths of the native land.

Our native worms may need their own King Under the Mountain to come and save the day!

This article was prepared by international exchange postgraduate student Nicola Wegmayr as part of the ECOL608 Research Methods in Ecology course.

The study this blog is based on can be read here. It is the source of most of the factual knowledge that has been included.

Boyer, S., Kim, Y.-N., Bowie, M., Lefort, M.-C., and Dickinson, N. (2016). Response of endemic and exotic earthworm communities to ecological restoration. Restoration Ecology, 24(6):717-721.

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