Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [116]
Two days later temperatures had dipped to -7°C, and no bees whatsoever were then venturing out spontaneously, providing an ideal opportunity to test their physiological limits. Poking a twig into the hive I generated a crowd of bees rushing to and congregating at the entrance. After a little more poking, I succeeded in provoking a few individuals to fly at and around me. I timed the flight durations of ten of them. Most nose-dived into the snow in just 2 seconds. None lasted over 6 seconds (the mean was 3.6 seconds) before it hit the snow, buzzed briefly, stopped moving, and then froze solid. Between takeoff and landing at flight cessation, the bee’s thoracic temperatures declined from 38° to 40°C at takeoff to 29° to 33°C (the mean was 30.9), right after they crashed when I grabbed them and determined their thoracic temperature with my electronic thermometer by the time-tested “grab and stab” technique. (Head temperatures would have been several degrees Celsius lower.) None made it farther than fifteen feet from the hive. After these measurements I agitated thirty-three more of them to leave the hive to see if any could make it back. None did. All fifty-five bees that I examined had the foul-smelling yellow paste in their rectums. My crude experiment showed that if they do leave at -7°C, which they were only willing to do in defense of the hive, they risk certain death. At what temperature would they risk flying out on their own?
On January 20 we had sunshine in the afternoon, although air temperatures remained low, near -9°C. But at about 2:30 P.M. the sun hit the hives broadside and bees started coming out spontaneously. In the half hour that I watched as an innocent bystander, 125 flew out. Every single one of these bees took its (involuntary) kamikaze dive into the snow after a few seconds of very rapid cooling in flight. Not one of these 125 eager leavers made it back into the hive. All solidified from internal icing. Most (112) of these bees had not voided their rectums, as I could easily ascertain visually by pulling open their abdomens. I was puzzled now, wondering: Why didn’t they defecate when they had the chance? They could not have flown out to commit suicide! Why had they risked death? I was determined to get to the bottom of this mystery. The next day, when it was warmer, I got another clue.
There was again a short period of sunshine in the afternoon. This time over three hundred bees had come out spontaneously—I found them dead and strewn all over the snow in front of the hives. All had died there, as before, since the snow was still near -6°C and so they all froze solid. Also as before, there was only modest fecal speckling on the snow; there was no soiling like one might expect if hundreds of bees had rushed out to relieve themselves. Were those bees at the entrance, the ones that rushed out, the subpopulation that most urgently had to relieve themselves but that died from cold before they had a chance? With that question in mind, I lifted a hive cover (the point in the hive farthest removed from the entrance) and retrieved fifty bees from the bee cluster just underneath it. All fifty of these had feces in their rectums, and I could detect no difference in the amounts they had from those in bees that had risked flying out into the cold. Neither did it seem that the abdominal temperatures of those outside had been too cold to perform their function; the abdominal temperature of those hitting the snow was still relatively high (11° to 19°C with a mean of 12° to 15.5°C).
Apparently the