It is perhaps a strange time of year to be writing about red mason bees but I have been investigating the results of the bees' nest-building in my bee house this past summer - of the many holes available three were used. I wrote before about the fact that several cells had been parasitised. I have now taken the bee house down to be stored in the shed over the winter so I had a look to see what has been happening before putting it away.
The bee in the observation wing completed eight cells. It turns out that only three contain bee cocoons and the others all contain one or two dozen maggots, presumably of the parasitic fly, Cacoxenus indagator.
In order to give the bees an advantage next year I discarded the maggots but left the bee cocoons in place, ready to emerge in May. The female bee lays all the daughter eggs first, so at the back of the hole, and the males at the front. I suspect all three here are female.
Two other holes were used. This one in a bamboo cane contained only fly larvae, with no bees at all.
This one in a raspberry cane had mainly fly larvae but a dark-coloured pupa in the front cell (top left in the picture). I doubt that it's a bee but it could perhaps be a parasitic wasp. I have kept it to see what it turns out to be but I have also discarded all the fly larvae. The cell walls in this nest are much paler so this bee presumably used a different source of mud.
So overall three female red mason bees built 21 cells of which only three (14%) contain bee cocoons for next year. Sadly two of the bees laboured in vain as all their cells were parasitised. I'm not sure if this is bad luck or if this is about the general success rate - it seems low to me. Maybe by getting rid of the fly larvae there will be more bees and fewer flies next year. Let's hope so.