A cob brick bee house

March is the time to look out for hairy-footed flower bees (Anthophora plumipes), one of my favourites.  They fly in spring, being among the first solitary bees to emerge from hibernation. They nest in cob walls and old mortar, often in large aggregations.  Their whole season is over by early summer and the next generation of bees waits in the safety of the wall before emerging the following spring to start the cycle over again.

I read an article in the BWARS magazine by John Walters, an entomologist from Buckfastleigh in Devon, on making a cob brick bee house for hairy-footed flower bees and was inspired to have a go.  A year ago I followed his recipe using cricket pitch loam mixed with a little sharp sand, some chopped straw and enough water to make it all stick together.  You can see John Walters' videos on how to make cob bricks for hairy-footed flower bees, part 1, part 2 and part 3.  I also took advice from my friend Chris Henderson, a retired doctor and renowned mud-brick house builder in Tasmania. Chris said the secret is to let the cob dry slowly, out of the sun, so it doesn't crack and fall apart. The bricks then have to be kept dry and put where the bees can find them.  I built a shelter from a few old planks and put it close to some pulmonaria plants, the bees' favourite flower.

I didn't see bees flying into the bricks while I was watching but within a few weeks there were signs of activity with what looked like spoil from excavation below a couple of the holes and at their entrances.

When I peered in at the end of the season with a macro lens and ring flash I could see something at the end of four of the holes.

My hope is that these are sealed bee nests.  I found a PhD thesis written by Radha Devkota Adhikari on the use of the hairy-footed flower bee for strawberry pollination in greenhouses in Japan.  It includes this photo of the inner structure of a nest and says "the inner walls of both provisioned cell and pre-chamber were coated white" so this could be what I am seeing in mine.

I have set up the bee house again, ready for the bees to emerge (I hope) later this month.  Ever the optimist I have also built a small cob-filled observation panel with a perspex window in the hope that I may be able to see what happens inside.  There are four small starter holes and if a bee does move in I'll keep my fingers crossed that it excavates next to the window so I can see what is going on.

I have also built a much more stylish Mark II version for the new season.  It contains Victorian land drain pipes filled with the same cob.  It is now in position in the hope that the bees will take to it.  If they do I'll post an update here.