This morning, nine dead worker bees were lying on the landing board of the Pond Hive. What - or who - killed these bees, so close to their own front door?

Actually, dead bees are quite a common sight on the landing boards, especially at this time of year. But they are particularly obvious against the fresh white paint of the Pond Hive's new stand.

Here are the possibilities I've considered:

The bees had been out, perhaps on an unsuccessful foraging mission, and on returning home they reached the landing board in a cold and exhausted state, and couldn't make the last few steps to the hive entrance.
As above, but they did make it to the doorway, only to be turned back by guard bees defending the entrance.
The bees had come out of the hive to take the air, and were overcome by cold when on the landing board.
They died (or were dying) in the hive and were dragged out by undertaker bees. Normally, undertaker bees carry the bodies some distance away, but in sub-zero temperatures I imagine they are keen to drop their cargo and return to the warmth of the colony as soon as possible.

Number 4 is my leading hypothesis. Worker bees in winter spend most of their time in the hive, so those that die probably do so in the hive. And there must be bees dying throughout the winter, of "old age" or disease. Also, notice that the bees on the landing board are lying upside down. If they had died where they stood, I think they'd still be the right way up.

I'd also been wondering about the pollen forager who is shown in the final photograph of this earlier post, lying dead on the landing board alongside the bodies of two drones. While the drones were probably refused entry to the hive, the same surely did not apply to the worker bee with baskets of nourishing pollen to offer. The worker must have died in the hive before she could unload her baskets, and then been carried out by an undertaker. As with today's bodies, the pollen forager is lying on her back and appears to have been dropped just a short distance outside the door in freezing temperatures. The drones, in contrast, are the right way up.

Agatha Christie: 9 Honey Bees