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Fauna in field drains

March 5, 2009

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:

Leech!

leech 2

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6 Comments leave one →
  1. March 6, 2009 1:12 pm

    Do rats may use them?

    I have had to ‘write up’ hundred of the bl**dy things, but it’s worth taking an interest, they can be 150 years old after all, and mark an significant event in a landscape’s history.
    It is well worth field archaeologists trying to understand the technology and dating of these features.
    A good starting point would be:

    http://en.wikipedia.org/wiki/John_Fowler_(agricultural_engineer)

  2. March 6, 2009 1:14 pm

    PS. Do you always excavate in white gloves?

  3. March 6, 2009 5:42 pm

    Rats? I suppose they could. Not these particlular drains though as I think there’s too much silt and plant debris for them to move about. I suppose it would depend on whether or not they could physically get in them and move about.

    John Fowler had some interesting ideas, didn’t he? I wonder if any of the ‘cuts’ for the capstan or pulleys have ever been recorded archaeologically. One of the pipe segements I exposed was stamped with a company name and location, so I’m going to do a little research, and may report back on the blog.

    As for the gloves, I don’t usually no, but at the time I was excavating a burial beneath the water table (and in a grave with a field drain emptying into it!), and I was tired of my skin cracking. Plus I enjoy impersonating Michael Jackson on site ;o)

  4. March 7, 2009 9:06 am

    – So its ” health and safety gone mad” – just a I suspected.

    Wondering what the leach was living off, if not rats or archaeologists, could it be voles, shrews, or mice?

    In the NE ‘U’ shaped drains with a cover predate circular types.

  5. March 7, 2009 1:21 pm

    I think I’d make a good health and safety fanatic. I’m not proud of that thought.

    Actually most leeches are predators, they eat (rather than suck from) smaller animals like earthworms. Although there was a study published in 2003 I think that showed that Erpobdella octoculata (which is what I think the leech I found was) are also fluid suckers that will attach to dead fish and newts, and that the young leeches will attach to wounded snails.

    On this site, the narrow ‘mole’-dug pipe drains are preceeded by hand dug, stone lined culverts.It would be a good site to contribute to a study of field drainage through the ages, if that’s your bag.

  6. March 7, 2009 10:08 pm

    Unless you have a theory that field drains are ‘Ritual’ you would never get funding!

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