Now that late summer is upon us, bumblebee nests are full of worker bees. These bumble-workers often stay out in the field at night, sleeping in flowers. I found this bee in a dewy Yellow Cosmos bloom. She was completely still, paralyzed by the cool morning temperatures.
Like mammals and birds, bumblebees are endothermic, meaning that they warm themselves from internal heat sources. Bumblebees do this by shivering their flight muscles as they wake in the morning. Until they reach running temperature, they are sluggish and can barely move a leg, let alone fly.
In the arctic, some bumblebees use their bodies’ heat to incubate eggs and young bees, just like a mother bird. Without a boost of maternal muscle-heat, the bees would not have enough time to complete their life cycle during the short arctic summer. This endothermic physiology explains why bumblebees, especially northern bumblebees, are furry: like birds (feathers) and mammals (hair), they have a layer of insulation to retain hard-won heat.
Our local bees’ nightly cold stupor saves energy. But immobility is is a dangerous habit, especially for footloose bees who like to sleep outside of the nest in exposed flowers. Yesterday, I watched a European hornet patrolling the profuse blossoms on a clematis vine. Every time it came across a bee or fly, the hornet lunged, trying to grab the victim.
Look sharp, little bee. An evil Puck is after your life.