Rain provides a hazard for bees, including the danger of being knocked out of the sky by a big raindrop. When it rains, the bees stay in the colony and survive on stored food. An extended rainy period can deplete supplies stored for the winter, endangering the survival of the colony. If foragers are caught away from their colony by a sudden rainstorm or cold snap, they sometimes take shelter under flowers or vegetation until the weather conditions improve enough for them to head homeward.
In the warm weather, bees are very active, but in winter they become sluggish and their metabolism slows. So-called warmblooded animals regulate their metabolism and maintain a relatively constant body temperature regardless of the temperature in the environment, and although cold-blooded creatures like bees and other insects are hot when their environment is hot and cold when their environment is cold, they do have some control over their body temperature through a process called thermoregulation.
Thermoregulation enables bees to adjust their body temperature by generating some heat when their environment is cool by, for example, shivering and crowding together. On cold winter days, bees keep warm by clumping together in large groups and beating their wings in order to produce heat, alternating positions on the colder perimeter of the cluster with their sisters who have warmer spots in the middle. The temperature in the center of the cluster averages 21 degrees Celsius (almost 70 degrees Fahrenheit), with a manageable range of approximately 12 to 34 degrees Celsius (54 to 94 degrees Fahrenheit). L. Fahrenholz and colleagues at the University of Berlin found that if the central temperature falls below about 15 degrees Celsius (59 degrees Fahrenheit) and the peripheral temperature is even lower, the bees are in danger.
The colony is more stable in the winter because the queen stops laying eggs and there are no fragile larvae requiring constant care and feeding. Honey bees can survive a normal winter sheltered in the hive, in a hollow tree, or in some other cavity, as long as they have enough stored honey to provide a source of energy. Most beekeepers only harvest the honey made during the spring and early summer for themselves, leaving the honey made from late summer and early fall flowering plants for the hive to consume during the cold weather. After the bees have eaten the honey in one part of the hive, they move in a cluster to another part where there is more honey. The bees tend to move from the lower honey storage areas of the hive (supers) to the upper supers during the winter. Some bees die when it gets too cold, and some species survive by migrating to warmer areas or by moving underground.
When external temperatures rise, bees increase the space between their bodies to help distribute the heat their bodies give off (metabolic heat), and they actively cool the hive in several ways. They may allow fluid droplets to evaporate from within their mouth to remove extra heat from the body, the bee's version of perspiration in mammals. When the colony is very hot, certain foragers will collect water, which they distribute in drops around the hive, and other bees will fan their wings to increase the air circulation and evaporate the water to remove some of the heat. When all else fails, the adult bees will hang as a group on the outside of the colony to totally remove their body heat from the brood area, a maneuver described by some beekeepers as a "beard." The hive would then be "bearded out," apparently wearing a beard made of bees.
The brood (the developing bees) needs to be kept at a stable temperature in order to grow normally, and during the summer season the temperature in the brood nest is maintained at 34.5 degrees Celsius (94 degrees Fahrenheit), with a range of plus or minus 1.5 degrees Celsius. Julia Jones and her colleagues, Madeline Beekman, Ryszard Maleszka, Ben Oldroyd, and Paul Helliwell, in Australia did experiments in which they transferred groups of brood cells into seven incubators that were kept at a different but constant temperatures, ranging from 31 to 37 degrees Celsius (87 to 99 degrees Fahrenheit). The brood cells were put into the incubators within one day of being capped, which indicates the beginning of the pupal phase. Seven days after the bees emerged from their brood cells, 378 bees were tested for long-term memory and 546 were tested for short-term memory.
To test the bees' memory, each bee was trained to associate a lemony scent with a reward of sucrose so that when the scent was detected, the bee would extend its proboscis in anticipation of the reward. Then they tested some of the bees after one hour and another group after twenty-four hours, to see if they extended the proboscis when they were exposed to the scent, which would indicate that the bees remembered the training experience. The study found that abnormal incubation temperatures had an effect on short-term learning and memory but that long-term learning and memory did not prove to be significantly affected by the temperature at which the pupae were reared. This suggests that there are some important neurological consequences of not maintaining the temperature within the desired range, and this could have some subtle impact on the development of optimal foraging ability.
Adult winter bees can live for several months, but when some die naturally, workers carry out their dead sisters and drop their bodies at a distance from the hive. On a warm day in the winter, bees will take cleansing flights. They do not defecate inside the hive, and indigestible material naturally found in honey and pollen accumulates in their intestines. If they cannot fly from time to time to eliminate waste from their bodies, they become ill and die. Some beekeepers remove the honey from small colonies during the winter, replacing it with high-fructose corn syrup, which is quite pure with no indigestible matter, allowing the bees to be kept for long periods without the need to void. In very cold areas in the northern United States and in Canada, some commercial beekeepers kill their bees at the end of each honey-gathering season and start the spring with a new package of bees purchased from a supplier. This strategy is not very common.
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