A couple of weeks ago two of us visited Minepits wood at Tablehurst for a natural history group meeting devoted to the animals of leaf litter and the soil. Though we’ve been recording species at the farm for the past couple of years, almost all of the creatures that have been observed have been above ground and we’ve not paid much attention to what is beneath our feet. Considering how important and fundamental the soil processes are to life in general, this is a bit of an omission, though since many of the soil organisms are very small and often hard to identify it is understandable.
The web of life in the soil is extraordinarily complex; starting from the energy source of the sun, the roots of plants push through the soil, help bind it together and are food for many animals. Bacteria have associations with roots, as do fungal hyphae, which in turn are eaten by protozoa and nematodes. Slightly larger organisms will feed on these, such as the barely-visible mites, springtails, pseudoscorpions, flatworms, and tardigrades, as well as those rather more familiar to us, including insect larvae, worms, centipedes, millipedes, slugs, and woodlice. Taxonomically, then, the soil contains numerous animal groups that we otherwise rarely see, so provides a good opportunity to come face to face with animal types that we may never have encountered before.
So, we spent probably an hour kneeling at one spot in the wood, on a very small-scale safari. To begin with it can be hard enough to find even the bigger creatures such as slugs and snails, but as you gradually accustom to the change in scale it becomes possible to find animals that are perhaps only a millimetre long.
There was only one slug in the patch we searched, and after working through the recently-published key, it turned out to be the short-keeled slug Limacus maculatus, which was a bit disappointing since that is one of the two slug species we have previously recorded at the farm. There must be more!
We also collected our first earthworm from Tablehurst, and ran it through the key. It was c 7cm long, with a tanylobic head with closely-spaced setae. The saddle appeared to run from segments 28-33. This was rather tricky, and I think it may be Lumbricus castaneus, though am not completely sure that it isn’t rubellus. I’m not especially minded to identify earthworms again! Slugs are easier.
There were also a couple of relatively easy-to-identify snails, the Rounded Snail (Discus rotundatus) and the perfectly-named Garlic Snail (Oxychilus alliarius) which does indeed smell of garlic. Three of the common woodlice species were also in the leaf litter: Common Shiny Woodlouse (Oniscus asellus), Common Striped Woodlouse (Philoscia muscorum), and the Pill Woodlouse (Armadillidium vulgare), plus the similarly tightly-curled (though completely unrelated) Pill Millipede (Glomeris marginata) and the common Striped Centipede (Lithobius variegatus).
Millipedes and centipedes are myriapods, and those two species are relatively large examples. When we started delving into the thin layer of soil at the surface other smaller relatives turned up. I assumed that this 2mm-long animal was also a centipede, but, though similar, it turns out to be a member of the Symphyla, a group of blind, translucent creatures in soil, only distantly related to true centipedes.
Then things got smaller. Spreading out a plastic sheet and lightly sieving some soil onto it meant we could find some of the soil mesofauna, primarily the springtails and mites, all of which are under 2mm long, and often considerably smaller; they are both very important and abundant parts of the biodiversity of the soil. The springtails (Collembola) are a group that used to be thought of as wingless insects, though recent DNA work suggests they are in fact more closely related to Crustacea! Identifying these got a bit easier a decade ago with the publication of the new key, though they are still relatively poorly studied, and there are few records even of the ubiqitous species. Even so, there are at least 300 species in the UK, but that is bound to be a rather inaccurate number. Still, with a bit of help and support from the national recorder Peter Shaw at the University of Roehampton we found at least five species, all of which are new records for this area, and many of them probably new county records: Orchesella villosa, Pogonognathellus longicornis; the dark form of Sminthurinus aureus; Lepidocyrtus lanuginosus; and Isotomurus palustris. The pictures show the rather wonderful diversity of this group.
Our quick bit of soil sampling also resulted in the collection of a number of mites (Acari). Now, this group is even harder to identify than the springtails. We will have a go at doing so at some point, but that may take some time. With well over 2000 known British species and undoubtedly many more as yet undescribed, this is an astonishingly little-known group. There is plenty of scope for gradually getting many more interesting and useful records of soil organisms at Tablehurst in the coming years.
Finally, we heard something rustling in the litter and it was a huge animal…