Why Beekeepers Prefer Large Colonies

When we visited the farm on Pomona this week, we saw two occupied hives.  The beekeeper told us that the smaller hive contained the weaker colony, and we chose to test our feeder with the larger, stronger colony.  The difference between these two hives made me curious as to what factors contribute to the strength of a colony, and why large colonies are preferred by beekeepers.

While wild bee colonies typically contain around 30,000 adult bees during the spring and summer, at the time of peak population, commercial bee colonies can contain as many as 50,000 to 60,000 bees.  The maximum size of a colony is partially limited by the size of its living space.  When the population becomes large enough and living quarters are so cramped that not all worker bees receive pheromones from the queen, they lay eggs to produce a new queen, which prompts the old queen and a large portion of the worker population to leave the hive and start a new colony.  Beekeepers can anticipate this tendency to swarm and thus retain their bees by splitting large colonies themselves and installing some eggs, brood, and workers in a "nuc," a small box with limited storage space for honey.  Workers in a queenless nuc will build queen cells on the eggs placed in the nuc and feed the larvae royal jelly, the strongest of which will grow into the queen for the colony contained in the nuc.

While swarming is a concern for beekeepers who keep large colonies, large colonies are still preferred over smaller ones.  A low-population domesticated colony with ample living space is considered "weak" because it eithrt lacks the foraging resources or reproductive ability to grow to full size, or it has befallen some hardship that has depleted its population.  This colony may be less fit than a larger colony, but hive boxes that are not fully populated are also susceptible to pests – such as hive beetles and wax moth larvae – that cause significant damage to the hive.  These pests greatly reduce the chance of survival of a weak colony.  We found a few hive beetles in the weak hive at Pomona, which wouldn't have successfully taken hold in the stronger hive.

An open hive well-populated with bees.

Interestingly, large colonies actually produce more honey per bee than smaller colonies, which gives beekeepers further incentive to let their colonies grow as large as possible.  A greater proportion of adult bees in large colonies act as foragers than in small colonies (perhaps because small colonies are more focused on rearing young bees to bolster the workforce than on gathering honey).  Additionally, foragers from large colonies have been shown to make more frequent foraging trips and bring back more nectar per trip than foragers from small colonies.  Since bees perform various tasks over their life cycles, the last of which is foraging, they essentially work until their bodies break down.  A large colony has a surplus of workers that must be reduced by wintertime (the population of domestic colonies shrinks to about 10,000 to 15,000 bees during the winter), so it might make more sense for individual workers in large colonies to work harder during their lifetimes for the benefit of the colony, but live shorter lives.  The result is that larger colonies produce a greater yield with respect to the number of bees they contain than smaller colonies.  The following are the approximate benefits of increased colony size:

• One colony of 30,000 bees produces 1½ times as much honey as the sum of two colonies with 15,000 bees each.
• One colony of 45,000 bees produces 1½ times as much honey as three colonies with 15,000 bees each.
• One colony of 60,000 bees produces 1½ times as much honey as four colonies with 15,000 bees each. (source: Pacific Northwest Extension guide to evaluating bee colonies)

Prof. Donaldson-Matasci's previous research has shown that not only do larger bee colonies gather more nectar per individual, but larger colonies benefit more from the ability to communicate in foraging for resources.  She kept small and large colonies (3000 and 6000 bees, respectively – an order of magnitude smaller than commercial colonies, so it is still unclear how these results scale) in alternating conditions where foragers could either communicate or not communicate the direction from the hive to a profitable resource (since bees orient their waggle dances with respect to the sun, keeping hives in diffuse light will disorient dancers).  She found that the detrimental effects of impaired communication on forage yield (measured as the change in the weight of the hive from day to day, which is mostly due to nectar) were greater for the large colonies than for the small colonies.  By comparing the number of bees that entered and exited the hive with the daily weight change of the hive, she also confirmed that individual foragers from larger hives gathered more nectar per day than individuals from smaller hives.  Analysis of traffic to and from the hive throughout the day suggests that larger colonies are able to find resources more quickly, allowing them to gather more from profitable resources before they are found by competing colonies (and defend those resources from competitors if necessary) and to more fully exploit short-lived resources, such as night-blooming flowers that wilt in the morning.  In the future, an automated feeder similar to the one we are building this summer could track visits from large and small bee colonies in the laboratory to determine precisely how much more quickly foragers from large colonies find resources, as well as how resource quality is judged differently in colonies of different sizes.

The reasons why large colonies perform better than small colonies are mostly unknown, although it is clear that the ability to communicate in order to coordinate the colony's behavior is critically important.  What is clear, however, is that large colonies do have an advantage over small colonies, both in commercial settings and in laboratory conditions that mimic the natural environment.  In a robust colony, individual bees contribute more to the well-being of the whole, encouraging the continued survival of the colony year after year.