Stelis phaeoptera and Osmia leaiana

In July 2014 I found two small black bees on Yarrow in my garden that I did not recognize. Searching my keys I identified them as Stelis phaeoptera, a cuckoo-bee species. It does the kind of thing cuckoos do, i.e. lays its eggs in the nest of another species, killing the young and taking its food. Its own egg then hatches and feeds on the pollen store.  It’s a well developed way of life among bees, practised by about a quarter of all species I have found in the Monmouth area.  Many more cuckoo bees, often beautiful insects, will appear in this blog, I hope.

This is now the third year I have found Stelis phaeoptera. In 2015 I found a second species, which I will describe in another post.

This bee not outstandingly beautiful. Falk’s name for it – Plain Dark Bee – just about sums it up. But it’s a neat insect in its own way: short-limbed, compact, heavily armoured and, of course, without any pollen brush. The integument is covered all over in what look like tiny pin-pricks.

The host in this case is most probably a bee which is common in my garden and for which I provide nest tubes: Osmia leaiana, the Orange-vented Mason Bee. It is about the same size and cylindrical shape – adapted to crawling into tubes – and a busy pollen gatherer. They are both fond of knapweed and scabious. Side by side the similarities are apparent:

All four British species of Stelis are said to be rare bees, and phaeoptera particularly so: ‘a much declined species’ according to Falk, with very few recent records. I am lucky to have it, even if its host isn’t.