Click the image for a larger look at what was already a very large bee buzzing around in the spring sunshine and briefly alighted on a windowsill. The Bumblebee Conservation Trust has a fantastic introduction to identifying UK bumble bees, from which I learnt a great deal and I hope has helped me accurately identify the example above as a Queen Buff-tailed bumblebee (rather pleasingly named Bombus terrestris in Latin).

Below, courtesy of Sigma's very fine 105mm macro lens, the rear leg from the picture above in extreme close-up (again click for a larger version). You can really see the sharp backward pointing barbs on the very end of the foot that anchor it to the surface. If you've ever had a large insect crawl over your hand this picture helps explain the spiky/prickly feeling you get.

Further up the same rear leg there is a large smooth, shiny flank bordered by hairs that is used for collecting pollen, as shown below. Apparently this distinguishes it from the cuckoo bumble bees, which have evolved to take over existing nests and not bother collecting pollen themselves.