Fauna in field drains
Being an archaeologist is a handy thing if, like me, you’re fascinated by nature, as we tend to spend a lot of our time in very close proximity to the ground and so get to see some very specific ecosystems. Recently, I have been excavating a large cut feature on a very wet, poorly drained, clay site. The site’s archaeology as a whole is one of occupation and attempts at drainage, with drainage somewhat dominating, from the Iron Age ditches, each with phases of recuts and subsequent fills, to the somewhat more modern fired ceramic field drains. The field drains are perhaps from the late nineteenth/ early twentieth century, and one of them cut my feature, which also happened to be deeper than the water table. As I removed the pipes in my feature, I noticed that the field drain was about seven centimetres in internal diameter, and still carries water, although is fairly thick with sediment and plant material. The field drains also support their own ecosystem, and I was intrigued at how this now-archaeological feature had become a distinct environment which supports life.
The first thing I noticed was a small crustacean which was carried out of the drain in the flow of water, and began happily crawling around at the (underwater) bottom of my cut. This was a water slater (Asellus sp., probably Asellus aquaticus L.), an isopod very similar to a woodlouse, but which lives in freshwater, usually in still or slow moving waters, and feeds on dead plant and animal material. Over the next two days, I noticed perhaps four more of these make their way out of the drain.
The other invertebrate large enough for me to spot was a leech of Erpobdella sp., which I rehomed using a small Ziploc-style bag. The leech attached itself to the bag using both ends of its body, and was quite difficult to remove. Leeches like this tend to eat other invertebrates, which might suggest there’s a whole lot more living in those field drains, although perhaps the Asellus are the prey. I think that of British leeches, only the rare medicinal leech (Hirudo medicinalis L.), will suck human blood, but I didn’t fancy using myself to experiment.
Unfortunately, I couldn’t get a clear picture of any of the isopods, but here are two pictures of my leech prior to release: