Earthworms

Earthworms have been in New Zealand for around 65.5 million years

In New Zealand, earth worms have developed into 200 unique species in this time. They are divided into three groups based on the depth that they live at:

• Leaf-Mould Earthworms that live on the surface in leaf litter,
• Topsoil Earthworms that live below the surface in the topsoil at shallow depths,
• Subsoil Earthworks that live below the surface at relatively deep depths.

Elusive and Large Earthworms

Most of the worms you find in your garden are not native earthworms but have been introduced to New Zealand by people. Native earthworms tend to live in remote areas or thick forest so not a great deal is actually known about them.

This one was found on a track by the lodge and is over 300mm long

While some earthworms are tiny, as small as 15mm long, the largest species, Spenceriella gigantea, found in Northland can grow up to 1.4m long.

Earthworms in the Tangihua Forest

Earthworms can be found throughout Northlands Tangihua Forest. The best place to look is in dense leaf litter, under logs, stones or in rotting logs. Sometimes they can be found on the tracks after a bit of wet weather.

Earthworm Physical Description

The three types of earthworms all look slightly different.

Leaf-Mould Earthworms

Leaf-Mould Earthworms are the smallest of the three types. They range in length from 15mm to 180mm but usually don’t get more than 50mm long. They are also the darkest coloured of the earthworms. This is because living on or near the surface they are exposed to sunlight and the darker colour helps protection them for the ultraviolet rays.

Topsoil Earthworms

Topsoil Earthworms are medium sized worms. They can range in length from 25 to 300mm but are usually between 75 and 200mm long. They are a lighter colour than the Leaf-Mould Earthworms, as they don’t require the same level of protection from the sunlight. Most Topsoil Earthworms are round however there is one species of topsoil worm that has an almost square cross-section.

Subsoil Earthworms

Subsoil Earthworms are the longest of the three types of worms. They can be as small as 32.5mm or as long as 1.4m. The largest of these species can be found in Northland. Thankfully they rarely venture to the surface so you are unlikely to wake up to one in your sleeping bag. Because they rarely come to the surface Subsoil Earthworms have no pigmentation so they are essentially clear.

Earthworm Behaviour

Leaf-Mould Earthworms

Leaf-Mould Earthworms do not make burrows as they spend their whole lives in the leaf litter on the surface. Although their dark skin provides a bit of camouflage they have no protection against hungry birds so they have become surprising quick moving for earthworms.

Topsoil Earthworms

Topsoil Earthworms spend much of their time in permanent burrows just below the surface. They aren’t as exposed to hungry birds as the Leaf-Mould Earthworms so they are a bit more sluggish. They will leave their burrows in order to find food, which they take back to the burrow to eat, or when it is time to find a mate. Some species don’t need to leave their burrows as often as they appear to be able to obtain food by ingesting the soil and absorbing the organic matter in it.

Subsoil Earthworms

Subsoil Earthworms spend almost all their time in their burrows so tend to be very slow moving. They will form extension networks of burrows moving in all directions through the soil. Some burrows have been found that are 20mm in diameter and extend more than 3.5m below the surface. They obtain their food from the soil, which may be why the burrows are so extension as they are searching for food.

How worms make their burrows

Earthworms have two different methods for making their burrows.

One method tends to be used when burrowing through more compact soils. The earthworms will swallow the soil to clear it out of the way and excrete it at the surface or in cracks, crevices or deserted burrows.

Another method is used for less compact soils. The earthworm extends itself out and inserts its front end into small spaces between the soil. The earthworm then contracts its muscles, expanding itself and compressing the soil around it. As they form their burrows they line them with a slime resulting in smooth walled burrows that are easy for the earthworm to move through.

Earthworm Distribution and Habitat

Earthworms are found all over New Zealand with different species preferring different habitats.

Threats and Conservation Plan

Native earthworms do not tend to survive once the forest has been cleared, particularly the Leaf-Mould Earthworms that rely on a constant supply of leaf litter. Some native earthworms are also being displaced by introduced earthworms that seem to be better at competing for food and space.

References

It is very apparent that specific information has been shared online between many organisations. Attributing to the initial source is impossible. As much as possible we have used our own photo’s and the following websites have been used as sources for our information.

• Te Ara The Encyclopaedia of New Zealand
• Wikipedia
• DOC website.
• T.E.R:R.A.I.N Taranaki Educational Resource: Research Analysis and Information Network