25 May 2013: Looking for Osmia bicolor bee

Leader: Richard Comont 

After a week of late-May rain, hail and sleet better suited to late February, the morning of the 25th May dawned sunny, bright and clear – ideal bee-hunting weather! We were looking for one bee in particular – the two-coloured mining bee, Osmia bicolor. Despite the name, it’s not one of the many bee species which nest in holes in the ground – rather, this attractive black and bright-red solitary bee nests in old snail shells. Once the bee finds a suitable empty shell (usually one of the banded snails, Cepaea sp.), it fills it with pollen and lays a single egg. At this point it does something almost unique amongst British bees: it begins collecting sticks, pine needles and grass stems and building them into a protective structure over and around the snail shell. When bringing the sticks back to the nest site, the bee carries them slung underneath its body, appearing to ride a broomstick, and it was this behaviour we were hoping to see.

I was slightly concerned whether the bee was still present at Radley – it was flying in at other sites, but at Radley motorbikers had eroded away the main 2012 nesting area over the winter, and I hadn’t found any during the previous weekend’s recce. At least, having recorded 137 species in a couple of hours the previous weekend, I was confident that we’d at least find something!

Despite the weather forecast, and the timing at the beginning of the half-term holiday, 11 enthusiastic volunteers arrived and we made a good start with flypasts from peacock and green-veined white butterflies (Inachis io & Pieris napi). As we reached the sun-trap in the lee of the bee’s favourite sand-hill, we found our first bumblebee – a queen red-tailed bumble, Bombus lapidarius. She still seemed to be prospecting for nest sites amongst the stones, an indication of how late spring has been this year.

Basking in the sun, we quickly spotted three different species of mining bee (Andrena carantonica, A. flavipes & A. nigroaenea), a plume moth (Emmelina monodactyla) and a beautifully-camouflaged tortoise beetle (Cassida vibex), looking just like a tiny six-legged version of its namesake. Freshly-emerged Common Blue damselflies (Enallagma cyathigerum) helicoptered overhead, but there was no sign of our target bee, so we moved up to the top of the hill.

We spread out across the hilltop, and found the jet-black female hairy-footed flower bee, Anthophora plumipes, a bright purple sloe shieldbug (Dolycoris baccarum), and a huge hairy Drinker caterpillar (Euthrix potatoria) – but still no sign of O. bicolor, an hour in and halfway through the allotted time. Then, at last, we spot one – a bright black-and-red ball of fur zipping between flowers. There’s no sign of its broomstick-riding tendencies, or of any nests, but it was encouraging to see that the population had survived both the wettest year in a century and the coldest spring since 1979. On the way back to the cars we find orange-tip (Anthocharis cardamines) eggs, and a miniscule larva: spring renewal, late this year, but progressing.

Richard Comont