One of the big knowledge gaps I want to address in my project (see PhD project page for background) is the distribution and characteristics of carabid larvae in the farm environment.
These charismatic little fellows haven’t been studied much, mainly because they live in the soil and therefore are a bit difficult to catch. The adults are easy to capture in standard pitfall traps (pretty much a cup set in the ground that they fall into); and some larvae get caught in these (as some species do come to the surface to hunt); but to sample the full community I really need to get down into the soil.
My initial idea was to take soil cores. This would involve removing a cylinder of soil, and sifting through for larvae. Though a tried and tested technique for study of soil biota, it is quite time consuming and heavy work! Whilst investigating how to get the best results for larvae sampling with this technique, a colleague, Chris Shortall, asked if I had considered subterranean pitfalls.
I had never heard of them, but they seem to be ideal to my purposes. The premise is the same as for standard pitfalls, but set beneath the surface of the soil, at the base of a tube of mesh that soil active invertebrates will fall into. Chris pointed me towards Mark telfer’s excellent guide (link at end), and Ian Sims for further info and advice. Mark and Ian both concurred that subterranean pitfall should be really useful for my sampling needs; and kindly advised on design, and related past experience (Ian has some papers out/soon on this). Based on all of this I decided to trial some subterranean pitfalls.
The main body is a 35cm section of drainpipe, with cut-out sections. Wire mesh is wrapped around and held with tie wraps. A bottle attached to drainpipe connector collects the samples, and can be hooked out up the pipe with a pole. Jon Storkey kindly jigsawed the drainpipe for the first trap, and Alice Milne and her husband Dan completed five more pipes to his template. I have the best supervisors ever. Then I finished them off with the sampling bottles.
On the 22nd January we got the traps into a wheat field on the Rothamsted estate. The soil there is pretty hard going, heavy clay with huge stones. But we persevered, and tried different ways of burying them with the soil auger and spade. One of the drawbacks of this trap is the long settling in period, what with the soil needing to level and butt up to the mesh. I will have to wait perhaps another week to get some useable samples- the suspense is killing me!
Mark’s Guide to Subterranean pitfalls: http://www.markgtelfer.co.uk/beetles/techniques-for-studying-beetles/subterranean-pitfall-traps-for-beetles/