Wednesday, 12 March 2014

Oil be back...

A slight diversion this week, and a step back in time to one of my former local patches.  When I first moved to Oxfordshire, in 2008, I lived in Headington, north-east Oxford, and spent a lot of time in Shotover Country Park, then ably managed by Shotover Wildlife.  I now live further away, in south Oxfordshire, but still visit Shotover from time to time to see Black Hairstreaks and other specialities.

Sunday evening was one such time.  On my way home from Savernake forest, as it got dark, I decided to go and see if I could find any Minotaur beetles – nocturnal big, black horned dung beetles found in great profusion on Shotover. 

Well, despite much searching, there were no Minotaurs to be found.  What I did spot, in the light of a fading headtorch, was a great big bulbous black thing - an oil beetle!  There used to be eight species of oil beetle (Meloe sp.) in Britain: three are now presumed extinct, two were thought to be extinct before being rediscovered in south Devon (and now survive in one and two sites respectively), two are widespread, if uncommon, and one is relatively widespread but even less common. 

This one was relatively small, out at night, with a wide (not square) thorax and a groove in the middle of the pronotum – that made it Meloe rugosus, the Rugged oil beetle!  Not only was it a species I’d never seen before, despite looking, but really quite a rare species in Britain with only a handful of Oxfordshire records.  When I got home I checked the records – one previous record from the site, in 1927, and astonishingly, in exactly the same 100x100m square!  After going missing for 87 years, the Rugged oil beetle was back on Shotover… and it had barely moved an inch!

Meloe rugosus - note the distinctive pronotal shape and groove

All the oil beetles share an amazing life-history.  Adult females – like my find – emerge, feed up, mate, and dig a hole in bare ground in sandy soils which they fill with thousands of eggs.  These emerge in spring, tunnelling up to the surface and climbing up onto flowers.  Here the larvae (known as triungulins, after their three-clawed toes) lie in wait for solitary bees.  When a bee arrives, the triungulins grab a hold, and hitchhike their way back to the bee’s nest, where they secrete themselves away in a brood chamber, eating their way through the stored pollen and the bee larvae themselves, before pupating and then emerging the following year, ready to start the process all over again.

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