In recent months, I have spent significant time writing about various aspects of the biology of honey bees. The articles included the members of a honey bee colony (June 2015), the components of a honey bee nest (July 2015), the external (August 2015) and internal (September 2015) anatomy of the honey bee, the tasks of a worker honey bee (October 2015), swarming behavior in honey bees (November 2015), mating biology of the honey bee (December 2015), and the honey bee sting (January 2016). In my March 2016 article, I will discuss honey bees as superorganisms. I will bring this series on bee biology to a close by synthesizing all of the articles I have written on this topic into a single article on honey bee biology (April 2016). I think understanding bee biology, or at least the basics of bee biology, makes people better beekeepers. Knowing what the bees are trying to do and when they are trying to do it allows you to adjust your management style such that your beekeeping goals and the goals of a honey bee colony overlap. In May 2016, I will go back to discussing beekeeping management topics.
If you look closely at the topics I am including in my series on honey bee biology, you will notice that there are two major items that I failed to discuss. These items, or behaviors, are colony level thermoregulation and the honey bee dance language. These are the topics that I am going to discuss in this article.
Of course, you might guess that these topics have little in common, other than the fact that bees are engaged in the behaviors and both behaviors ensure the survival of the colony. However, I thought it best to include them both in the same article, if for nothing more than to introduce you to the intricacies of two amazing group behaviors performed by honey bees. I include at the end of this document a list of references that I used when compiling the information I am presenting to you herein. In particular, I relied heavily on Seeley’s (1985, 1995) and Winston’s (1987) books on honey bee ecology/biology/behavior. However, I include a few other references that I believe you will find helpful if you wish to explore either topic in greater detail.
Overview of Colony Thermoregulation
The ability to thermoregulate is one of the greatest attributes of the honey bee colony. When it is cold outside, honey bees can keep their colonies warm. When it is hot outside, honey bees can cool the nest. These simple truths cannot be overstated because they are what make honey bees, particularly the cavity-nesting honey bees, able to live in a range of environments and promote nest homeostasis. This feat is especially pronounced in the honey bee species we keep, Apis mellifera.
Depending on whose side you take, there are nine or so honey bee species on the planet. Four of those species (A. florea, A. andreniformis, A. dorsata, and A. laboriosa) are open nesting honey bees, meaning that they live on single combs that they suspend from tree limbs, cliff overhangs, etc. These honey bee species are, somewhat, at the mercy of the environment as their nests are exposed and vulnerable to the whims of Mother Nature. Consequently, these species are distributed mainly in the tropics of Asia, particularly Southeast Asia, where the genus as a whole calls home. There, it is warm much of the year so cooling the nest is not such a high priority.
The other five honey bee species (A. mellifera, A. cerana, A. nigrocincta, A. koschevnikovi, and A. nuluensis) all preferentially nest in cavities, though some members of these species will build exposed nests. This movement toward cavity nesting allowed these species to inhabit different climates than those to which their open-nesting cousins are confined. In particular, A. mellifera, the western honey bee – the bee we keep, has fine-tuned its cavity nesting behaviors, so much so that it can be found in near-desert environments all the way to the coldest temperate ones. This happens because it can thermoregulate its nest.
A single honey bee is a cold blooded insect; but the honey bee colony is warm blooded creature. It can make its temperature different from that of the surrounding environment, and this makes it one of the most unique of all the insects. I like the way that Jones and Oldroyd (2007) put it:
…part of the ecological success of social insects (all termites, ants, and some wasps and bees) is that they have at least some ability to regulate temperatures within their nests. This allows them to be physiologically active when other insects might be too cold.”
Bees are so good, in fact, at thermoregulating colonies that they can keep the colony within a 33 – 36°C (91.4 – 96.8°F) temperature range when the ambient temperature falls within a range of -40 to 40°C (-40 to 104°F). They are fine tuned to detect small temperature fluctuations, doing this with the temperature receptors on the five distal (end) segments of their antennae. They can, in fact, detect a temperature difference of 0.25°C (0.45°F). Thus, they can tell when the colony is getting dangerously hot or perilously cold.
How Bees Warm Colonies
The western honey bee’s normal distribution is from northern Europe, through the Middle East, and down to the southern tip of Africa. As you might imagine, the environments represented within these latitudes are among the most extreme on earth. Honey bees nesting in these areas, especially in Europe, have developed effective ways of warming the nest when the nest is too cold. They warm the nest for a couple of primary reasons. First, brood (their developing young) develops best around 34.5°C (about 94°F), with an acceptable range being between 32 – 35°C (89.6 – 95°F). The brood rearing temperature varies by less than 1°C daily. Any deviation from this temperature, even a degree or two, can have dire consequences on the developing brood or the adult that results. In fact, few bees emerge below 28°C (82.4°F) or above 37°C (98.6°F). At these extremes, the emerging bees usually have malformed wings and mouthparts, abnormal behaviors, and short lives. Second, optimum brood rearing conditions allow brood to develop faster, thus helping foster rapid colony growth in spring, colony recovery after swarming, and colony recovery after being attacked by pests or predators. Third, keeping the nest warm allows bees to be ready to fly when necessary. Like for all other insects, cold-blooded bees must reach a certain temperature before they are able to fly. Otherwise, cold colonies would be hard to defend and cool temperatures would prohibit the bees from foraging for food. Fourth, the ability to warm colonies has allowed honey bees to maintain populous colonies through winters, thus allowing them to inhabit colder climates. This is very important because where the warming trait is absent, as in A.m. scutellata (the “African” honey bee), the bees cannot survive temperate winters. Finally, the ability to raise the nest temperature allows colonies to get fevers, much like humans do, in an attempt to overcome pathogen infections. Thus, the nest must be heated.
Honey bees heat the nest these two primary ways: via passive thermoregulation and active thermoregulation. Passive thermoregulation is accomplished, in part, by the overall structure and architecture of the nest in which they reside. For example, bees select nest sites that allow them to optimize the internal nest temperature. These cavities often facilitate internal air movement, have small entrances (<60 cm2 or 9 in2) toward the bottom of the cavity, have insulated walls (the walls of a tree cavity, for example), are elevated at least 3 m (about 10 feet) from the ground, etc. Bees will seal drafty cracks or unwanted, small, holes with propolis. The nest cavities also must be a minimum volume (usually around 15 liters or 4 gallons, but preferentially about 40 liters or 10.6 gallons) so that there is sufficient space to store adequate, insulating honey around the nest core (Figure 1). Honey bees usually keep their brood in the center of the nest and surround it with a thin layer of pollen and a much thicker layer of honey, all stored in sheets of wax comb. Pollen, honey and wax act as insulators for the developing bees. Finally, queens often lay eggs on the side of the nest that is warmest. I often see the brood area shift in winter to the sunny side of the nest, likely to help keep it warm. All of these qualities help the bees thermoregulate the nest passively.
Bees also warm the nest actively. This means that they engage in behaviors that allow them to modify the nest temperature physically. They use two main behaviors to do this: directly incubating brood and clustering. Warm bees are able to incubate brood cells directly by pressing their warm thoraces onto individual capped brood cells in a crouching posture. They also heat brood by entering empty cells adjacent to cells containing brood so that their warm thoraces can radiate heat in all directions. This way, a worker is able to warm up to six brood cells at one time.
The second way that bees warm the nest is by …