This morning's visit enabled us to make contact with all our target species, including Heath Bee-fly (Bombilius minor) which was way too mobile to be photographed. Several were Lifers for A and I.
Bee hotels provide me with endless enchantment – from the first hatchings of the new bees in spring, to the constant hum and movement of the adults as they prepare their nest tubes and lay down the next generation.
I have several types of bee hotel, lying along the length of a low brick wall. Two of the shop bought variety, filled with bamboo cane, which have steadily disintegrated with constant weathering. A solid wood, “bee-hive” with removable shelves, and a set of three short birch logs, whose ends I drilled.
I was unsure how the birch logs would fare, having put them out for the first time this year. They were occupied almost immediately by nest hungry Osmia bicornis.
Part way through May, O. bicornis numbers were building up and all the hotels were being utilised. I also noticed a handful of small flies, on and around the brick wall, sitting on the edges of the bee hotels, and flying in and out of the bamboo tubes.
I posted some images of the fly on the UK Diptera Facebook Group, asking for an identification.
Cacoxenis indagatar
It did not take long before the fly was confirmed as Cacoxenus indagatar. This species is a cleptoparasite of mason bees. It lays its eggs in the nest cells of the host, and when its larvae hatch, they feed on the pollen laid down by the mason bee. As a result, the bee larvae might starve to death – or even get eaten by the fly larvae, should numbers or size of pollen store dictate.
To escape the cell walls of the O. bicornis the adult fly, has a neat trick. It can inflate its head, to force a breach in the wall, a feat it may have to undertake several times to escape along the length of a nest tube. Hence it earns its vernacular as The Houdini Fly!
New Scientist [Online] has a video of the great escape artist in action:
