Why are bees dying outside my door at night?

One possible answer is that bees are attracted to bright lights, even at night. If there is a beehive anywhere near your house, and you have a porchlight on at night, bees may be attracted to the light and then not be able to find their way back to the hive. So they die in the evening chill. or run out of fuel flying around the light all night, and then collapse. You could try putting your porchlight on a motion sensor, and see if that helps to alleviate the problem.