October 30, 2015
Honeybees are one of the few insect types that survive winter as a colony. Honeybees do not migrate, nor do they hibernate. So how does the hive survive winter? Answer: it shivers.
Shivering is an adaptation of so-called “warm-blooded” organisms. Warm-blooded organisms rely on their own bodies to generate heat and maintain a consistent body temperature. Human beings are quite familiar with shivering in cold environments. A shiver is really a series of rapid muscular contractions. These rapid muscular contractions burn energy and produce heat. This heat helps maintain consistent body temperature in cold environments.
Honeybees, however, are so-called “cold-blooded” organisms. Cold-blooded organisms rely on their environments to provide heat. They have no adaptations such as shivering to maintain a consistent body temperature.
So, if a honeybee is a cold-blooded organism, then how is it possible for a honeybee to “shiver?” The answer is that a honeybee on its own is a cold-blooded organism. The hive as a whole, however, acts as a warm-blooded organism.
A hive gets ready to shiver starting in the summer. Shivering requires fuel, and “summer bees” work in a frenzy to provide this fuel. The summer bees gather nectar and produce honey. If the stockpile is not large enough, the hive will not last through the winter.
“Winter bees” take over during the colder months. The bodies of winter bees are different than the bodies of summer bees. Winter bees are fatter, since foraging is scarce. Winter bees live longer than summer bees--four to six months, as compared to forty-five days. When the temperature dips below 54 degrees Fahrenheit (12 degrees Celsius), it is the job of the winter bees to surround their queen and shiver.
Before the hive can shiver, the bees must pack themselves onto the honeycombs. This “winter cluster” expands and contracts as the weather warms and cools. A cluster might be as small as a softball or as large as a basketball.
The shivering begins when the honey bees activate their flight muscles in a special pattern. The muscles pump to burn fuel and produce heat. The honey bees gather in layers and rotate position for insulation. The core of the cluster surrounding the queen can range in temperature from 64 degrees to 90 degrees Fahrenheit.
All of this pumping requires fuel. As the winter wears on, the clusters moves inside the hive, consuming the stockpile of honey. The burn-off of this fuel is carbon dioxide and water vapor. Carbon dioxide is heavier than air, and escapes from the hive’s bottom exit. Water vapor escapes from the hive’s top exit. A blockage of either of these exits can prove disastrous for the hive. A carbon dioxide buildup can poison the colony, and water vapor that cannot escape will drip onto the cluster as ice-cold water, severely compromising the cluster’s ability to feed and maintain warmth.
So, the next time you happen upon a beehive on a cold winter day, know that the bees inside are shivering just as much as you are to stay warm.