Red mason bee report

It is the time of year for tidying up and taking stock.  I have brought in the bee house in for the winter and I took the opportunity of seeing what the red mason bees (Osmia bicornis) have been up to.  The photo above shows a male bee searching for a newly emerged female last spring.  One very industrious female bee moved into the top row of the observation wing and completed 15 cells.  Here are the first three cells, each containing an egg and a pile of pollen for the larva to eat.

The bee lays female eggs first, at the back of the nest, and males towards the front because the males emerge first in spring.  Males are smaller so their cocoons and cells are also smaller.  I think this nest originally had eight females and seven males although the front few males were taken by a bird - probably a woodpecker - but the others survived.  This is the view before I removed the perspex.

Without the perspex I can use the flash for a clearer photo.  The repairs a bit lower down were done after previous woodpecker damage.

These two cells contain red mason bee cocoons.

These two have been parasitised, probably by the cleptoparasitic fly Cacoxenus indagator.  Inside the frass in each cell were several small white maggots.  I expect the larvae overwinter and pupate into flies in the spring.

I prefer bees to flies so I took the opportunity of clearing out the parasitised cells.  I left all the cocoons in place so in order to escape in the spring the bees will have to chew through the mud walls as well as their cocoons.  This might slow them down a bit and give me a better opportunity to video and/or photograph their escape.

It also allows a closer look at the cell walls made from mud (hence the name, mason bee).

This year I also tried out some cardboard tubes with paper liners.

Here is a photo from May showing a female bee inspecting a the tubes.

I think only one tube was used - the yellow staining is from pollen.

When I opened the paper liner I found three mason bee cocoons and two unused pollen pellets.  No parasites in this one.

Several raspberry canes in the bee house were used as well.

I opened these two to have a look inside.  Usually the bee starts building at the far end but one here seems to have started half way along.  Her nest contained three cocoons and one parasitised cell.  The other one was completely parasitised (and so was discarded). 

Other bees used holes in the wall of the house, holes in dead tree trunks and holes drilled in wood blocks in the bee house but obviously I can't investigate those.  This was in the bee house in spring.

It was an interesting spring this year because by the time the mason bees emerged in early May it was already warm and there was a very short interval between the first males and first females.  I think the female bees got on with nest building very early, perhaps giving the Cacoxenus flies less time to react.  Certainly the parasitisation rate seems lower than I have seen before.  With luck there will be more red mason bees than ever next year.