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The Roving Microscope - Fieldnotes #3

Drawing illustrating the layers of Danielle's wormery

Wormeries are commonly designed to include perforated trays, allowing worms to bioturbate (burrow, ingest, and defecate) through layers of organic matter as they do in the wild, and to help make mature compost and 'worm tea' (liquid fertiliser) easier to harvest. Worm bioturbation plays an important part in maintaining soil quality, and was first studied by Charles Darwin in the 1800's.

This week Danielle gave us two samples from her wormery, one from the top layer (the feeding ground!) and one from the bottom, where the worms tend to nest in more fully composted material. We studied these samples under the microscope to see if they were noticeably different in any way.

Microscope image of an oribatid mite (magnified x100)

Interestingly, when we looked at the top layer, the first thing that came into view was a family of microarthropods grazing on organic matter.

Microarthropods are really important members of the soil food web, they eat decaying plant, animal and fungal material and help to shred organic matter and aerate the soil in much the same way worms do. These particular microarthropods are Oribatid mites (we think) which are quite common in soil surfaces, particularly inhabiting leaf litter, moss and lichen. They eat fungi, algae and decaying plant matter, but some also feast on live nematodes and dead springtails. Ants, beetles and some larger animals eat the oribatids, they also look pretty similar to the cheese mites we showed in our last blog!

On the top layer we also counted a record-breaking number of nematodes, around 90, and around 10 ciliates (single-celled organisms with little hairs which propel them around) – all in just one drop of soil solution under a slide.

Microscope image of a nematode (magnified x100)

Microscope image of a ciliate (magnified x100)

As we looked deeper into the wormery, at a sample from the bottom layer, we noticed much fewer oribatids (only 1 compared to around 5 in the top layer), fewer nematodes (around 20), but much more ciliates (50 ish, though they are hard to count and photograph, because they whizz around so fast!).

This suggests that the bedding layer might be a bit less oxygenated and wetter than the upper layer, as ciliates particularly like to feast on anaerobic bacteria, or, that the top layer has more tasty food available, attracting the nematodes and microarthropods to the feast.

Watch this space for more microscopic adventures with the Roving Microscope!