November is here, and the temperatures are going to range from the low 30s at night to high 40s in the day this week. What does that mean for bees? No one leaves the hive without great danger to themselves.
Bees will venture out and forage short distances on sunny and windless days when the temps are in the low 50s, but they physically cannot stay out in cooler temperatures.
Studies have shown that worker bees need a thorax temperature of at least 77 degrees — that is where the flight muscles are housed — to produce a wingbeat frequency enough to generate sufficient lift for flight, according to entomologist Bernd Heinrich’s 1993 research. These studies have also shown that a worker honey bee cannot keep her thorax temperature more than 27 degrees above the air temperature during prolonged flight. This is why honey bees are rarely seen foraging at air temperatures below 50 degrees. But as we will find out, there are always exceptions!
Cornell University professor Tom Seeley and Ann Chilcott conducted an experiment in January and February 2017 that showed honey bee foragers collecting water at air temperatures as low as 39.2 degrees. Bees visited the water source on 22 of the 27 days.
On the 22 days that the water collectors were active, the lowest air temperatures recorded were 39.6 F to 40.1 F or higher. On the five days that the water collectors were not active, the highest temperatures recorded 39.2 F or lower.
So, how did the bees in this study they observed collecting water at 40 degrees manage to maintain the minimum thorax temperature of 77 degrees that they needed to fly home?
Shivers
A 2010 study by Anton Stabentheiner, Helmut Kovac and Robert Brodschneider used an infrared camera to continuously measure the thorax temperatures of water collectors while they were drinking from a water source 10 to 30 feet away from their hives.
When the bee is loading up on the water, she activates her flight muscles (shivers) to keep her thorax temperatures always above 95 degrees. These flight muscles and shivering are the mechanism that produce the heat inside the hive that keep the bees warm all winter.
These investigators found that water collectors maintain this high thorax temperature over a broad range of air temperatures from 37 to 86 degrees. The study suggests that the reason the honeybee keeps her thorax hot while loading is to keep the suction pump (cibarium) in her head functioning efficiently and lowering the drinking time even at low temperatures. Presumably by preheating her flight muscles by shivering, she is precharging the “batteries” that will enable her to make a short flight home, before her muscles lock up and she falls to the ground.
Many bees can be found dead in the snow on a warm January thaw while out on their cleansing flights. Some of the bees were already dead inside the hive, and other bees were doing housekeeping in the hive. This is part of the science that may explain why some bees never made it back to the hive as their flight muscles locked up in the cold temperatures. After hitting the snow-covered ground, they couldn’t produce enough heat to continue back to the hive. When the temperatures are cold and snowy in northeast Ohio, follow the bees advice in the winter: “Shelter in place” and read the Farm and Dairy!
