Honey Bee Castes
Worker (left), drone (middle) and mature queen (right). Photo by Zach Huang.
During the summer, a Langstroth hive colony consists of 40 to 60 thousand adult bees. During the winter, a typical hive will have around 20 thousand bees including one queen and few to no drones. Like most living things, bees haves two sexes, either female (queen and workers) or male (drones). Within the two sexes, there are 3 castes of bees within any colony: the queen, the drones, and the workers.
The approximate breakdown by caste is:
* 1 queen.
* 100 - 300 drones.
* 26 - 40 thousand in-hive bees (young workers).
* 13 - 40 thousand foragers (oldest workers).
The brood, comprising of eggs and young is typically:
* 5 - 7 thousand eggs.
* 7 - 11 thousand larvae.
*16 - 24 thousand pupae.
The queen can lay up to 2,000 eggs a day during the height of the laying season. She does not lay from November through January.
The relationship in any one hive is quite complex with the queen being sister to some and mother to others. With the queen mating with many drones, there are three possible levels of among female siblings: those with the same father are super sisters; those with fathers who are brothers are full sisters; and those with unrelated fathers are half sisters. The result is a hive with varied genetic origins.
The queen is the only sexually developed female in the hive and is the largest bee in the colony. While the queen decides the sex of her young, workers select which fertilized eggs become queens. In other words, queens and worker bees start out the same, the difference being the larger queen cell accommodates the larger size of the larva and pupa that result from the difference in diet queen larva is fed. While both worker and queen larva are fed royal jelly for the first three days, the queen receives royal jelly for her entire larval stage. Receiving royal jelly during her entire larval stage allows the queen's hormone/pheromone producing glands, and her reproductive organs to develop fully. She is one and a half times larger than a worker, with an elongated abdomen. The queen is fed only royal jelly for her entire life.
Queens are not treated as queens until her pheromone glands become fully functional after successful matings. While queen can mate with up to 40 drones, the average is about 12. The more matings a queen has, the more her pheromones change, and the more acceptable she is to the workers. A queen is sexually mature when she is six days old. Orientation flights near the hive, beginning at about 1 week, allow her to learn the landmarks and strengthen her flight muscles. The stronger her muscles, the longer she can fly, allowing more matings. A queen flies further than drones thus limiting the possibiilty of inbreeding. If, for whatever reason--such as bad weather, a queen does not mate during her second week as an adult, she will be past the mating age, and the colony will replace her.
Workers push, cling to, and pull on the virgin queen's legs and wings in effort to get her to leave the hive for her maiden flights. The attacks subside when she returns to the hive, but begin again before the next flight. They continue until the queen starts laying eggs.
With only one queen available at a time for maiden flights and with the continued existence of the hive dependant upon her, the queen does not take her maiden fights alone, but is accompanied by a host of worker bees. She is too valuable accomodity to be out in the world on her own. She doesn't know the land marks, plus there is safety in numbers as far as predators are concerned. Almost 100% of virgin queens return safely to the hive.
During April and May, the queen lays day and night, each egg taking about 20 seconds. That's over 2000 eggs a day, more than the body weight of the queen. The queen inspects and measures the size of each cell with her front legs before deciding to use it. Drone cells are deeper and wider than worker cells. It is the size of the cell that tells the queen whether or not to fertilize the egg she lays in it. While the queen fertilizes the eggs that become workers, it is the workers who guide the queen to the empty cells, and in essence are also responsible for the sex of the brood.
The pheromones produced by the queen have many effects within the colony. Most obvious is the retinue response to her in which the workers lick her and rub their antennae on the queen. It also encourages the workers to feed and groom her. Through this behavior, workers acquire and distribute the queen's pheromones throughout the colony regulating the activities of the hive such as inhibiting reproduction by workers, control swarming and regulate worker tasks critical to colony growth and survival.
Queens can live for 5 years, though they are generally replaced in managed hives every other year as their egg laying capability diminishes over time due to depletion of their sperm bank. Due to pesticide use, she may live as little as 6 months, necessitating vigilance on the beekeepers part.
The drone's sole purpose in life is to mate with a queen insuring the survival of the species, and if successful, his reward is death. His sexual organ, which is barbed, is ripped out upon completion of successful mating and he falls to the ground dead. This allows the queen to obtain 100% of the drone's sperm. A queen will mate several times on each flight. The succeeding drone will remove the apparatus left in the queen by the previous drone before mating. Back at the hive the house bees remove the apparatus left by the last mating of the day.
Drones are not able to mate until about 16 days of age. When drones have reached maturity, they start orientation flights to learn the landmarks near their hive. Drones tend to congregate daily in the afternoons, in packs called comets. Comets can contain anywhere from a few hundred to thousands of drones. The open areas they frequent are called DCAs (drone congregation areas) and the same area can be used year after year by subsequent generations. One DCA at Selbourne in Hampshire, UK was first described in 1789 and still exists today. Drones may embark on as many as 25 flights during their lifetime with each flight lasting from 30 minutes to an hour. They may make several flights in an afternoon, flying back to the hive to re-energize on honey. Drones in DCAs tend to fly at certain heights and within certain boundaries. The drone congregation area can range anywhere in size from 100 to 700 feet in diameter and be 30 to 130 feet in the air. Other insects entering the area are chased by drones. While they will also chase anything thrown in the air above them, they will not chase a queen who is outside of the DCA. The number of colonies represented in a DCA has a direct influence on the genetic diversity of the queen's offspring.
While drones are pretty much considered free loaders as they do no work, they are not totally without some benefit to the hive. Their presence may provide an additional sense of well-being in the hive, as some drones may be allowed to over-winter in the hive. All bees, including the drones, will work to bring the hive temperature back within normal hive limits when they sense a deviation in temperature. Another side benefit is the varroa mite prefers the larger drone brood as it guarantees a longer development period for its own offspring. The number of varroa mites can be kept in check by removing the capped drone brood and destroying it either through freezing or heating the brood comb.
While drones produce no wax, perform no in-house chores, do not forage, nor defend the hive (they have no stinger), they are tolerated by the hive only on the off chance a new queen needs a mate. Come fall they are driven from the hive to die either from starvation, predation, or exposure.
Workers, like the queen, have 2 sets of chromosomes (32), one set (16) from their mother and one set (16) from their father. Workers are the backbone of the hive upon which the welfare of the entire colony depends. They do all the work and attend to all of the queen's needs. The type of work they perform is dependant upon their age. In a normal colony, the bees do the work best fitted to their age, but they can do any work required after they are ten days old. Despite this well established pattern, the age at which specific tasks are performed is extremely flexible, as bees are able to accelerate, delay or reverse their pattern of behavioral development to meet the needs of the colony.
Workers are house bees for the first three weeks of life. Their various duties include maid, nanny, royal attendant, undertaker, heating and cooling specialist, and guard. Another duty that has recently been documented is that of heater bee. http://jeb.biologists.org/content/206/23/4217.full