Yesterday we found about 20 honeybees dead in the snow near some hives in Durham City, and immediately jumped to the conclusion that some new catastrophe was befalling these useful insects. But a bit of Googling around beekeepers' web sites suggests that it ain't neccessarily so.
Apparently dead bees are quite common around hives in winter but when they are scattered in the grass and withered leaves they usually pass unnoticed. Opinion seems to be that they are there for two common reasons for this winter mortality. One is that on sunny days, even in the depths of winter, members of the hive remove the corpses of dead bees and dump them some way away, as part of their winter housekeeping. The other possibility is that bees' metabolism ticks over during winter and waste material accumulates in their hind gut, so they occasionally leave the hive on bright days just to defaecate; some don't make it back before the cold gets to them. Given that all of these dead bees were in a few metres of one another, I'd go for the former explanation in this instance.