I blogged about Dark-edged bee-flies earlier this month but, since then, I’ve noticed one doing something odd so thought I’d share what I’ve since found out about what it was doing. I spotted an area of miniature soil volcanoes where mining bees were active, digging out the tunnels in which they would lay their eggs, and, nearby, a sweet little bee-fly flicking its own eggs in to the holes of the bees it predates.

Then, that same bee-fly started hovering in one spot, frantically beating its wings but going nowhere (see video below). What was it doing? I asked on Twitter, and one of my followers suggested ‘It could be filling its rear-end up with sand’ – not a sentence I ever thought I’d read! But this was sort of right.

Someone from the Soldierflies and Allies Recording Scheme referred me to their website entry for bee-flies, which explains that ‘the adult females collect dust or sand at the tip of their abdomen, using it to coat their eggs, which helps protect the eggs from drying out.’ I’m guessing the sandy coating also means the eggs roll more easily into the bees’ tunnels. It was a fascinating insight into what is an extraordinary lifecycle, though I can’t help but feel some sympathy for the hard-working mining bee victims.