More on bumblebees

Posted: Sunday, September 06, 2009

The alpine meadows were lively with bumblebees zooming from flower to flower. It was the only decent day in an autumnal week of gray and gloom and downpour, and the bees were taking full advantage.

Earlier this summer, I was captivated by bumblebees sleeping in fireweed flowers and began to wonder about their behavior. So I read some scientific reports about these furry pollinators, and learned that the workers often do not return home at night. And I also learned some other interesting tidbits; here are a few of them.

Bumblebees are unusually good at regulating their body temperature. Birds and mammals usually control body temperature close to some particular value. We humans, for example, normally control our body temperatures at 98.6 degrees. Bumblebees, however, can regulate the head, thorax and abdomen temperatures at different levels simultaneously.

At rest, a bee's temperature is close to the environmental temperature. But it needs a temperature of about 100 degrees to fly well. A bumblebee flies in cool weather by raising the temperature of the thorax to the required level.

The shivering of the thoracic muscles is not visible externally, but one can tell if a bee is warming its flight muscles by observing the abdomen, which is pumped to ventilate the hard-working muscles.

A queen bee raises the temperature of her abdomen when she incubates her eggs, which she does by sitting on top of them, rather like a hen. Arctic bumblebee queens even maintain high abdominal temperatures while the eggs are developing inside their bodies, effectively incubating the eggs before they are laid.

By doing so, it speeds up development and produces workers more quickly -to exploit the short Arctic summer.

Incubating eggs costs a lot of energy, especially at low environmental temperatures, when the egg temperatures need to be kept much higher than the outside temperatures. For example, at 15 degrees or less, it costs as much to warm the eggs as it does to fly - about seven or eight times the cost of incubation at 85 degrees.

Incubating queens can feed themselves from the honeypots in the nest, where they and workers have stored the nectar they gathered. The honeypot, like the rest of the cells in the nest, is made of wax secreted from between the abdominal segments of the bee, and sometimes the wax is mixed with pollen.

Unlike honeybees, bumblebees reportedly do not collect and incorporate plant resins in the waxy cell walls. The honey stored the honeypots is about 90 percent sugar, so the bees have concentrated the collected flower nectar, which is generally less than 40 percent sugar (e.g., fireweed nectar is about 30 percent sugar).

Postscript: In my earlier column on the colorful fungus called chicken of the woods, I reported that two friends had apparently become very ill after eating it for dinner.

I later learned that a local doctor told my friends that a short-term flu-like bug was circulating among Juneau folks at that time, causing digestive distress. It was therefore possible that chicken of the woods was totally innocent in this case. Nevertheless, the usual cautions apply.

• Mary F. Willson is a retired professor of ecology.

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