Middle left: 3 channels used by an Orange-vented mason bee (Osmia leaiana), R: close up of Common yellow-face bee (Hylaeus communis) Photos taken when unit was removed in October
For for the first time this summer, we inserted a summer unit into our solitary bee observation nest box in our garden. They have various size holes to attract different species of cavity-nesting solitary bees during the summer.
It was very exciting when our first bee arrived; At first we thought she was a Blue Mason bee (Osmia caerulescens), because they are fairly common and divide up their cells with chewed leaf. But with the help of Twitter, she was correctly identified as an Orange-vented mason bee (Osmia leaiana) by the orange pollen brushes on the underside of her abdomen. A new species to me!
That was in July, and the video we posted of her busily making her cells and provisioning them with bright yellow pollen went viral.
Just below the Orange-vented mason bee, a smaller, shiny black bee with yellow markings on its tiny face moved in. This Common Yellow-faced bee (Hylaeus communis) started to do something incredible, lining her cell with a cellophane-like, waterproof substance. Each egg is laid inside a cell which resembles a see-through plastic bag filled with a mix of nectar and pollen for the larvae to eat.
Heatwave and drought…
We left the bees to get on nesting, but were concerned how they’d fare during the heatwave and drought. We couldn’t move the unit to a shadier, slightly cooler spot because the adult females wouldn’t be able to find it. Would mum struggle to find nectar from drought-hit plants? Would her eggs, and/or larvae be boiled alive in the heat? Would she?
When we finally removed the summer unit at the beginning of October, with a view to cleaning it out for winter, we could see lots of pollen in the area being used by Osmia leaiana and the Hylaeus communis larvae still developing in the waterproof sacs.
So, are they OK?
None of my books prepared me for this, so I contacted George Pilkington, creator of the summer unit and bee expert, Ted Benton for their thoughts.
Orange-vented mason bee
George told me that in his experience Osmia leaiana can sometimes take two years to develop! “I have found this as quite a few times I thought they had died and binned them only to find some years later that left to their own devices, they emerge the second summer. I know of others who have had this too. Now I leave them in the cavities and let them get on with it. “
Ted was a more concerned: “If there is still a lot of pollen in the cells, the larvae will not have developed. I’m not clear why that would be. Possibly the eggs didn’t hatch, or maybe there wasn’t enough nectar mixed with the pollen for them to gain their full nutritional requirements.” Ted suspects that many summer-flying solitary bees have found it difficult to deal with the drought this year because “the key problem has been lack of nectar for food and moisture”.
Verdict: Not sure
Common yellow-face bee
Both confirmed that the Hylaeus communis larvae looked OK. “They have consumed all their food supply and appear to be in the ‘mature’ larval stage as ‘prepupae’. They will remain in that stage over winter, and then pupate and emerge late spring/ early summer,” advised Ted.
George Pilkington has a fantastic video of the life cycle of the Common Yellow face-bee here that confirms they don’t make cocoons like the mason bees we are more familiar with.
Verdict: Yes
As a result, we have decided not to clean out the unit. We have put it back in the observation box and put them in the shed where they will keep cool and dry over winter. We will see what happens what happens next year.