The Bee that Lived in a Snail Shell

Talking of bees...

This morning's The Living World reported on the tiny bullet-shaped Osmia bicolor, a sort of mason bee which seeks out empty snail shells for a nest. 

This was another delightful programme from Trai Anfield.

Trai was walking around the chalk downlands of Dorset with naturalist John Walters. And not just any old chalk downland. 

No, they were investigating the hillside directly above the the Cerne Abbas giant [the famous chalk figure that depicts the Palestinian Authority president in a decidedly frisky mood].

The scene sounded lovely. They were investigating a very steep, south-raising slope full of yellow cowslips and vibrant purple orchids, with a horny chalk giant below them and bees buzzing above them. 

John put out some empty snail shells on the slope last year, and awaited developments. The bees nested in them.

So why do Osmia bicolor bees nest in empty snail shells? 

Well, other mason bees love crevices and snail shells, especially on chalk downlands, are the closest things to a crevice that a bee can find. Plus there are plenty of them around.

Males hide in the shells if the weather gets too cold, but they don't stay for long as they are very short lived. The longer-lived females nest in them. 

Osmia bicolor are solitary bees. Even if they nest quite close, they only interact for mating purposes and that closeness is out of necessity rather than choice.

The females lay their egg in the snail shell then start camouflaging it, giving it a green, speckled appearance. They do that after mating. 

They select a nest site [snail shell], build a little nest, collect pollen to feed their soon-to-be larvae (using the special hair of the underside of their abdomen for extra efficiency), then lay one egg and surround it with mashed-up leaves, then collects rubble, soil and more mashed-up leaves to pack the remaining spaces, tightly seal it, turn he shell over so that the entrance is pointing downwards and then make an elaborate 5-6 cm long tent of grass ["a little wigwam of grass stems"] to hide the shell. It only takes a hour or so to do.

Trai described the result as "a work of art" that "just blends in beautifully".

Unlike many other insects,  Osmia bicolor lays a mere 10-15 eggs in its lifetime. They may lay a handful each year, each in a separate snail shell. They have a high survival rate. 

This represents a rather typical pattern in reproduction - you either spend a lot of time and effort to keep a few offspring safe and sound, or you produce so many that losing a few doesn't matter much. 

John said that there's been little study of them, little written about them. There aren't any identification guides for solitary bees yet.

Still, there's The Living World - and this blog!