Red-tailed Mason Bee

So I am busy trying to photograph a Duke of Burgundy butterfly when I get photo bombed by a bee dressed in bright orange safety gear and carrying a big stick. It has to be worth further investigation.

A big stick for a little bee

It turns out that the bee is a Red-tailed Mason Bee - Osmia bicolor and it has an unusual nesting habit. Males appear in early spring and defend a small territory containing empty snail shells. The females arrive a couple of weeks later and once mated they build one or more nest cells in the shell using vegetation and mastic (chewed up vegetation). They then seal the shell with a plug of earth, stones, shell and more mastic. The snail shell is then moved to its final location, turned so the entrance is facing the ground and sometimes part buried.  Mastic is painted on the outside of the shell and it is then covered, by the females, using vegetation and small sticks.

Carefully placed

I had missed the first part of the process, arriving on the scene when the female was busy concealing the shell. She started by dropping sticks and vegetation onto the shell but as the cover grew she took to placing items into the build to better improve the cover.

Flying in broomstick style

She also appeared to be using saliva or mastic to hold the construction together.

Selecting a spot

and maneuvering into place

Not quite right so takes it out and tries again

A lot of effort goes into the build process, probably a lot more than is required just to cover the snail shell. Given that the female could construct five or six nest sites like this during the breeding season, I assume that this type of structure offers better protection against predators and parasites.

Fascinating to watch but the sad thing is, that the nest is being built in Kithurst Meadow, a very popular Duke of Burgundy butterfly location. It is already well trampled and the chances of this nest site surviving must be slim.