In most cases this isn't something to be alarmed about. In fact, it means your bees are healthy and they are doing what they should be doing, cleaning out the hive. Bees die all winter long, just not as often as they do in the warmer months. Those dead bees on the ground in front of the hive (easy to see on snow) are just the dead bodies that the rest of the hive is removing in order to keep their home clean. You will notice it even more when we get those odd warm days of 40