| Earthworms of New Zealand |
| Interesting fact |
| Different earthworms, different homes, & different jobs |
| Earthworm biology |
| Benefits of the mighty earthworm |
| Encouraging earthworms into the garden |
Earthworms
Earthworms are segmented worms that are scientifically classified as belonging to the phylum Annelida (ringed animal). There are 3500-4000 species of earthworms around the world. They are full of calcium, protein, fibre and vitamins, making them a valuable food source for many mammals, reptiles and fish. Earthworms vary in size, ranging from 1 centimetre through to about 1metre in length. One of the world’s largest earthworms, the Giant Gippsland Earthworm (Megascolides australis), is found in Australia. It has an average length of over 1 metre.
There are nearly 200 different species of identifiable earthworms in New Zealand. Most of them are native but a few were accidentally introduced by early settlers from Europe in soil used as ship ballast as well as potted plants.
Native New Zealand earthworms are bigger and more vulnerable to disturbance than the introduced species, and they tend to populate less frequently disturbed areas.
A New Zealander discovered that the total weight of all earthworms below a pasture is similar in weight to grazing animals supported above ground.
Different earthworms,
different homes,
and different jobs
Earthworm species play different and unique roles in the soil environment.
There are four main types of earthworms in home gardens:
- Compost dwellers. Like to live in high organic matter environments such as compost heaps, but will not usually survive in soil unless it has a very high organic matter content.
- Soil surface dwellers. Feed on decaying roots, shoots, leaves and dung and live near the soil surface (0-15 cm depth). Important in mixing plant litter into the soil.
- Topsoil dwellers. Most common earthworms in New Zealand; live in the top 20-30 cm depth of soil. Burrow through soil, eating and excreting it; tend to eat more soil than organic matter.
- Subsoil dwellers. Tend to live in permanent burrows up to 3 m below the soil surface; drag food such as leaves into their burrows from the soil surface; often larger than other types of earthworms.
Earthworms wriggle underground with the help of tiny bristles (setae) along their outer surface and discharge a slimy lubricating mucous. Their strong muscles convey swallowed soil and organic residues (e.g. micro-organisms and partially decomposed plant and animal material) found on the soil surface to the gizzard. Stones that were swallowed and the strong muscles of the gizzard then grind up these materials and pass them through to the intestine where digestive juices act upon the material and release organic molecules such as amino acids and sugars. Some of this is absorbed into the bloodstream and the remainder, along with undigested waste, is excreted by worms as castings or ‘worm poop’.
Benefits of the mighty earthworm
| Enhance soil fertility Note: through digestion of organic matter |
Improve soil structure Note: through movement and feeding |
| Incorporate surface litter and speed up nutrient recycling | Increase the mixing of soil layers |
| Encourage mixing of nutrients, fertiliser, and lime through the soil profile | Enhance water infiltration· |
| Increase nutrient availability to plants through digestive fluids together with increased microbial activity in the casts (droppings) | Reduce erosion |
| Increase the decomposition rate of organic matter by burying around 6 tonnes of pasture litter per hectare· Increase plant growth | Increase moisture holding capacity |
| Increase plant growth | Increase plant growth by facilitating plant root penetration |
| Help control diseases, e.g. apple scab disease · | Facilitate the break down of root mats in pastures and thick layers of leaf matter |
Encouraging earthworms into gardens
- Maintain soil pH between 5.8 and 6.3 by adding lime periodically to the soil.
- Limit the amount of cultivation where possible. Avoid machines that pulverise the soil and the earthworms contained therein.
- Use garden forks rather than spades.
- Limit the use of harmful pesticides (particularly fungicides and fumigants).
- Irrigate the soil during dry periods to maintain earthworm activity.
- Increase organic matter in the soil by incorporating composted material or animal manure. Otherwise, earthworms will migrate if there is a lack of organic matter present.