Jennifer Wood and her husband Robert Steffes keep bees. Over the years they have been not only great sources of information about these wonderful animals, but also they have kept me well supplied with the jars of honey I need to get my blood sugar elevated enough each morning to face the new day!
Jennifer responded to the “Migrate, Mutate, or Die” blog (Signs of Winter #5) by describing the adaptive strategies their bees (European honeybees, Apis melifera) employ to survive the winter. European honeybees do not hibernate, but instead stay active throughout the long, cold winter months. The honeybees cluster around the honey combs inside of their hives and shiver their flight muscles to generate heat. The temperature inside of a bee-warmed hive can reach as high as ninety degrees F (although optimal temperatures would not be nearly that warm!). The cluster of shivering bees moves up (never down!) the honey comb so that they continually encounter fresh honey to fuel their muscle contractions and heat production. These bees also rotate individuals from the very warm middle of the shivering cluster to the less warm, more stressful outer edges in order to spread the impact of the winter’s thermal stress over the entire group.
European honeybees, then, are primed and ready for the first hints of spring weather and are able to move right into pollen and nectar gathering as soon as temperatures and the first waves of spring flowers allow. This ability to immediately respond to the bounty of spring is a significant selective advantage for the species.
There is a downside to this overwintering strategy, though. Two years ago I wrote about the impact of a warm, late winter on honeybees that triggered their early emergence into a world in which no plants had yet flowered. These bees spent a large amount of their limited energy reserves in futile attempts to find nectar and ended up gathering almost anything that might substitute for their natural foods (one gentleman in Latrobe wrote me about bees completely cleaning out his cracked corn bird feeder!). Without extra feeding by a beekeeper, these bees would be very likely not to have sufficient food to survive the remaining cold days and nights of the winter and early spring.
The overwintering strategy of the honeybee, then, sits in a very delicate balance between great success and absolute failure! The European honeybee, though is only one type of bee out the twenty thousand known species, and many of these other types of bees have very different “solutions” to surviving the winter,
I went to a web site that listed the common insects of Pennsylvania (insectIdentification.org ) and noted the types of bees likely to be present here. The site listed the European honeybee, four species of bumble bees (Bombus spp.), and two species of carpenter bees (Xylocopa spp).
Bumble bees, like European honeybees, live in colonies. The sizes of these colonies, though, are quite different. A domesticated honeybee colony can contain up to eighty thousand individual bees during the peak of summer activity. A bumble bee colony, though, usually has less than fifty individuals. Toward the end of the summer new queens (fertile female bees) and fertile male bees mature in the bumble bee colony. These fertile individuals emerge and mate, and then the males die shortly thereafter. The mated queens, though, continue to feed on flower nectar and pollen and find crevices, holes, or even sheltering flowers in which they can spend the night. They steadily build up considerable body energy reserves that will see them through the long winter.
Eventually, as the summer fades and the cooler nights of autumn signal the coming winter, these queens find more protected places (often abandoned mouse nests or burrows in sandy soils) where they can hibernate. They go into a physiological state that enables them to slowly use their energy stores as they wait out the long, cold winter months. Early in the spring, these queens stir from hibernation and begin to forage for nectar and pollen among the early spring flowers. Their large body sizes and extensive coverings of hairs enable them to retain heat even in air temperatures that would seem to be too cool for insect activity. In the early spring these great, floating bees fly about close to the soil surface in their search for flowers. They must be careful, though, not to misjudge their rate of energy use or the lateness of the day or they might get caught out away from their hibernaculae and end up freezing in the cold, night air.
These bumble bee queens eventually establish their summer colony site and begin to lay eggs. The small cohort of workers that develop, then begin to assist the nurturing and survival of the colony. A bumble bee colony only lasts one season, so it is imperative that enough food resources be gathered to fuel the production of the next generation of queens.
Carpenter bees (Xylocopa spp.) are solitary bees (they do not form colonies although in some species the sisters and/or the daughters of a fertile female may continue to nest together in a simple social group). Adult carpenter bees drill branching cavities into wood (and can be the cause of a great deal of damage to buildings and homes), but they do not eat the wood. They discard the woody debris (or use it to make partitions inside of their woody nest) and rely on nectar and pollen for their food. Carpenter bees are important flower pollinators and many people have made the decision that the wood damage they cause to homes or barns is small price to pay for all of the essential pollinating work these bees accomplish.
Adult carpenter bees hibernate in the woody burrows in which they were born and in the spring, emerge and mate and either continue to live in those nests with their extended female family members or strike off and establish new woody burrows nearby. The male carpenter bees live solitary lives outside the nests and visit flowers to gather their individual food requirements. They do not, however, enter the nests at night or contribute to the groups’ accumulation of pollen or nectar.
Bees, then, survive winter in a variety of ways. They can be adults shivering together, waiting for warming temperatures. They can be mated, hibernating queens sleeping through the snow and cold. They can also be un-mated males and queens hibernating in their parental nest burrows.
I can’t wait to see the spring bumble bees drifting about like little zeppelins or the swarms of honeybees clustering over the first flowers of the spring! We have more winter to get through first, though! Hang in there!