This weekend a friend brought a bag of worm compost. Ticks all the great gift boxes!
So, of course it had to go under the microscope. But – what is this? Worms visible to the naked eye? They look rather pale, 10-20mm long. Hmm.
Got them under the scope, 40X total magnification.
I did not think earthworms looked so spikey. After a quick scare, when someone suggested these could be intestinal worms, I did a bit of calm thinking. The source ingredients, all veggie except for some chicken eggs, suggested it’s unlikely, even though the eggs could be contaminated with some chicken poo. And the microscopic images I could find of chicken parasites did not match. Back to the drawing board.
We settled on probably enchytraeid, though could not totally exclude it may be earthworm babies. However, this compost has Red Wrigglers, and the very pale colour made me conclude enchytraeids.
These small worms belong to the mesofauna, we don’t need to use the microscope to spot them, but have much more fun when we do.
Key learning points:
- Apparently they feed on already finely broken down plant matter, on fungi (large proportion of their diet), and a little on other microbial tissues, as they don’t have the complex enzymes that the earthworms have to digest more complex plant matter. It is probable they further break down the worm castings, so this also points to the presence of enchytraeids in vermicompost as logical.
- Enchytraids can be found globally, but are thought to have emerged in the temperate regions
- Their common English name is Potworm, because they are often discovered when potting on plants, when using moist compost (the proper stuff!)
- Typically 2-20mm long, though some can be up to 50mm.
They have no pigments.
- They occur in many habitats. Abundance fluctuates with the seasons, highest numbers in spring and autumn. This may relate to soil moisture content, as they are aquatic organisms, relying on a film of water in the soil.
- They don’t have specific structures that protect them from dry conditions, so are reliant on reasonable moisture (or may migrate to such soil regions).
- Higher numbers seem to be found in forests compared to agricultural soils.
- Didden & Fründ have a useful habitat and species table; different species seem to tolerate different soil ph, and prefer different soil textures
- They seem to predominantly feed on microbes, but can, to some extent, feed on dead organic matter, but this needs to be sufficiently small
- It is likely there is, at least for some species, an interaction (direct or indirect) with root excudates and/or decaying roots
- They can be found at different depths, typically where there is the highest concentration of organic matter. Thus, in ploughed soils, where the soil is turned upside-down, they are at deeper levels (?possibly also related to moisture)
- Where earthworm numbers are higher, enchytraeid numbers may be lower according to some research, and vice versa, but also show optimal development at different temperatures and moisture levels, thus using different ecological niches
- Some mites and nematodes feed on enchytraeids, also some insect larvae
- Similarly to earthworms, they create burrows where soil is sufficiently moist, lined with their secretions, thus impacting soil structure, water and air distribution positively
- Their excrements, alongside that of soil microarthropods, seems to constitute a large proportion of the humus in moorland
- There is evidence that they were plant-protective, where strawberries were impacted by root-feeding nematodes, but also had a negative impact on pine seedlings in a nursery, where many enchytraeids were found in the compost
- They seem to be less vulnerable to tillage than earthworms, probably because their burrowing structures are on a much smaller scale, possibly also because they are so small, more may escape the chopping actions of the plough.
- They can be susceptible to application of different inorganic fertilisers
- Whilst they can bounce back from single applications of herbicides or pesticides, repeated use will reduce their numbers
What makes a good gift? For me, something that inspires curiosity, keeps me engaged for more than a fleeting moment, and the longer you spend time with the gift, the more you appreciate it. And, at the very end of it’s or my time, it’s compostable. Thanks Sue!
Further introductory reading in David C. Coleman et al.’s (ed.) “Fundamentals of Soil Ecology”, and quite a bit more detail by Wim Didden & Heinz-Christian Fründ on Enchytraids in an older publication (1997), available here.
And some beautifully captured photos of enchyntraeids in their natural habitats by the very talented and dedicated Andy Murray.
As always, I may be wrong. Someone suggested these could be insect larva.
However using this key to insect larva, I concluded enchytraids are more likely.