I was recently sent this intriguing question from a reader:
Dear Dr. Dolittle,
I heard in my science class that because honeybees have such high blood sugar levels, they can survive freezing…is that true?
To answer this question, I turned to expert Dr. John G. Duman from the Department of Biological Sciences at the University of Notre Dame who studies antifreeze proteins in insects. Here is what he had to say:
In short, no.
Insects generally survive subzero environmental temperatures by evolving one of two strategies. Some are freeze tolerant, meaning that they can survive the freezing of their body fluids. In contrast, those species that die if frozen must evolve seasonal adaptations that prevent freezing of their body fluids in winter, such as various antifreezes that make them freeze avoiding. (For a recent review of this topic see the book Low Temperature Biology of Insects, edited by D. L. Denlinger and R. E. Lee, Cambridge University Press, 2010). However, honeybees are neither freeze tolerant nor freeze avoiding. They die of hypothermia if their body temperatures are lowered to approximately 7 degrees C. In fact, they are endotherms. Like humans and other mammals, they control their body temperatures by producing internal heat, mainly by shivering their flight muscles. In addition, they huddle together into a large mass that conserves the heat produced by the individual bees. Individuals within the cluster move in and out between the center and the outside edge of the cluster. This combination of endothermy and clustering keeps their body temperatures well above freezing right through the winter. In one experiment, when the air temperature around the cluster was kept at 5 degrees C, bees at the center of the cluster had body temperatures of 35 degrees C and temperatures of individuals on the outside edge were approximately 19 degrees C. The center of the cluster generally stays between 30 and 35 degrees C even at outside temperatures as low as -30 degrees C.
A number of insects, especially bees, wasps, and certain large moths are endothermic during the warm months, using the heat produced as a by-product of the flight muscles to maintain their thoracic temperatures. However, very few species remain endothermic through the winter. One serious problem for maintaining endothermy at low temperatures is that it becomes very energetically costly, requiring large amounts of food. However honeybees are able to remain endothermic because the honey that they have stored generally provides a sufficient energy source to get them through the winter.
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