Busy as a Bee

The temperatures the last few days have been below average for this time of year.  This morning at 8:00 it measured 50 degrees Fahrenheit (10 degrees Celsius).  These lower temperatures have caused many insects to remain inactive until later in the day, but not the bumble bees.

Common Eastern Bumble Bee (Bombus impatiens) nectaring on Nodding Wild Onion (Allium cernuum)

This Common Eastern Bumble Bee (Bombus impatiens) was busy foraging on Nodding Wild Onion (Allium cernuum) flowers in the Winn Elementary Pollinator Garden.  Like other insects, the body temperatures of bumble bees is tied to that of the ambient air temperature.  As the air temperature rises so does their body temperature; conversely, as the air temperature lowers so does their body temperature.  This means that if the air temperature is low, many insects are inactive or very sluggish.  To be able to fly a bumble bee's flight muscles must be at a temperature of 30 degrees Celsius (86 degrees Fahrenheit) - with an air temperature of only 50F (10C) this bee should have been inactive, but it was busy flying from flower to flower.

How is this possible?

Like humans (and many other animals - see my post on the Black-Capped Chickadee), bumble bees are able to shiver to warm themselves.  In cold temperatures, bumble bees can uncouple their flight muscles from their wings and vibrate them rapidly - the wings themselves do not move, only the muscles.  On a morning like today's, it may take them approximately 5 minutes to warm their thorax enough to enable flight.  During flight their thorax easily maintains this temperature (30-40 degrees C/ 86-104 degrees F), but when they land their body temperature begins to drop.  To maintain the ability to fly, at each stop the bee must continue to shiver.  This ability to regulate their own body temperature to a small degree means that bumble bees are able to remain active in air temperatures that ground most other insects.

For more information on the bumble bees get a copy of the book Bumblebee Economics by Bernd Heinrich, Ph.D.   Dr. Heinrich is a professor emeritus of biology at the University of Vermont.  His doctoral research focused on the body temperatures of bumble bees.  He later expanded his research (and that of others) to write Bumblebee Ecomonics.  I highly recommend any book by Dr. Heinrich - he is by far my favorite nature writer working today.