Bee ‘bearding’ describes when a bee hive takes extreme steps to cool the hive. Thousands of bees can hang off the entrance (like a beard), fanning cool air into the hive. By hanging on the outside of the hive, they also reduce the heat load within the hive itself.
It’s not surprising that my hive generated an impressive beard earlier in the week, on the 37°C day that was the hottest October day for Sydney in all of history. What was fascinating (and somewhat scary!) was how the bearding grew during the day (see below).
Apparently this also means I should add a sixth (!) box to the hive, to reduce overcrowding.
PS. apparently the day-time temperature peaked at 4pm that day, which would explain the crazy amount of bearding. (While the bees are on a relatively exposed roof, they do get shade for most of the day from nearby trees.)