Probably Osmia leaiana or a ‘pesto bee!’
A medium sized summer bee which has a bright orange pollen collecting brush (scopa) on her underside abdomen. It is also known as the Orange-vented Mason bee. As she does not use pieces of leaf (Leafcutter bee) or mud (Red mason bee) to make her brood cells, she uses masticated plant material which gave rise to my school pupils in Liverpool calling her the ‘pesto bee!’ Great descriptive name!
This is the second time (2013) this bee species has successfully made cells in my nest boxes. I have seen the rudimentary beginnings of several pesto style nest linings and rear wall, but for some reason they were never completed, along with several unsuccessful Blue mason bee nest cells. So this year I am very happy to welcome at least one female back!
For info and link to buy an excellent book Field Guide to the Bees of Great Britain and Ireland by Steven Falk
An extremely useful resource supports this book by a special web site feature within Steve Falk’s Flickr web site which furnishes extra photos and other useful resources to assist with identification.
For more information about solitary bees visit BWARS
Interested in Citizen Science and pollinators? The Buzz Club