Sunday, 23 February 2014

Beetling about in flood debris

Anyone who's not been living under a rock for the past two months can't fail to have noticed that the country is slightly damp at the moment.  Large chunks of Somerset, Oxfordshire, Berkshire and others have been underwater as rivers reclaim their flood plains, while the sheer volume of water has saturated the soil, leaving rainwater pools on the surface.

Of course, floods are horrendous when they affect your property, family or livelihood, but if you're interested in insects and other invertebrates, they can also provide something of a bonanza.  Huge numbers of invertebrates - snails, harvestmen, beetles, and more -  live in the soil, amongst roots, in leaf litter or at the bases of grass tussocks, and at this time of year they're joined by a whole load of extra species that go there to spend the winter.  When the water rises, these invertebrates are flooded out and washed downstream with all the other flotsam and jetsam - litter, sticks, etc.  This all accumulates in heaps of debris around obstructions, and picking through these mounds can turn up all kinds of species.
Flood debris collecting between the bank and a narrowboat
My local river, the Thames, has been flooded to varying degrees since Christmas, and I've been out a few times to see what's been washed up.  The main groups  have been beetles and snails, both terrestrial and freshwater.  Probably the pick of the 27 species of snails that have turned up so far has been the ribbed grass snail, Vallonia costata - a species I'd only ever seen once before, at last year's Bristol bioblitz.  Although it's only 3mm long, the ribbing combined with Mick Jagger lips makes it both distinctive and (for a snail), really rather attractive.
Vallonia costata, photographed down the microscope
Something I hadn't ever seen before was a tiny but very smart harvestman, Nemastoma bimaculatum - black and leggy with two white flashes (hence bi-maculatum).  By far the biggest fraction in the debris  has been beetles, particularly carabids (ground beetles) and staphs (rove beetles), but some smaller stuff has turned up as well.  Some has been impressively small - one that I've yet to do anything with is a featherwing beetle, family Ptiliidae, well under 1mm long!  Because there's so many beetles they're a bit on the back burner until my PhD corrections are finished, but all the other species, plus a bit of judicious lichen-spotting in the back garden, have taken my 1km square list up past 300 for the year - well on track for four figures by year's end!
Nemastoma bimaculatum from flood debris
A still-mysterious featherwing beetle, Ptiliidae sp. Image width approx. 1.5mm!
Flood debris beetles waiting to be identified - mostly carabids, particularly Bembidion spp., but also Heteroceridae, Aphodius, Hydrophilidae, mostly Cercyon spp., and some Chrysomelidae in tribe Alticini

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