There are three castes in a honeybee colony: the queen, the worker and the drone. There is only one queen per colony and she will live for about three years. During her reign there are numerous workers although the numbers of workers per colony fluctuates with the seasons reaching a peak in early summer and dwindling to a minimum in the depths of winter. In the early summer the colony begins to produce drones who emerge to live the life of Reilly until the end of the season when they are forcibly evicted to die in hungry heaps in the long grass.
The details of the control of the complicated demographics of the honeybee colony are for another day! Only the mechanisms of how the colony manages to produce three castes from two sorts of egg will be dealt with below.
Cross your fingers and click table for bigger picture.
There are three phases of development – the egg, the larva and the pupa.
All three castes come from eggs laid by the queen, however the queen can only lay two kinds of egg – fertilised and unfertilised. Fertilised eggs become females, that is workers or queens, while unfertilised eggs become males – the drones. So the egg-type sorts out the most fundamental differences between the castes – sex. Unfortunately there are only two sexes and three castes so something else must cause the differentiation of queen and worker.
Honeybees build three sorts of cells for their queen to lay her two types of eggs in.
- Small hexagonal worker cells;
- Large hexagonal drone cells;
- Downward pointing, cup-shaped queen-cells.
It is not known how the queen knows to lay fertilised eggs in small hexagonals and unfertilised eggs in large hexagonals but Hooper suggests she measures the cell top with her forelegs then acts accordingly. All fertilised eggs can become either queens or workers but it depends entirely first of all on how they are housed and secondly how they are fed subsequently which influences larval development.
All honeybee eggs hatch after 3 days into small crescent shaped larvae whose mission in life is to eat-eat-eat. To this end they are fed bee-milk by the nurse bees. Bee-milk is produced by glands in the heads of the nurse bees and it contains just what a baby bee needs for healthy growth and development.
Drones and worker bees are fed as much as they can eat for about 3 days after which they receive smaller daily rations until the cell is sealed, drone cells having domed cappings which help accommodate their larger bulk. Cells are sealed between 8 and 10 days, drones taking slightly longer than workers and queens (see Table 1.).
While the workers and the drones are getting their bee-milk rationed, the larval queen or queens continue to float in it in their deluxe, queen size cells and continue to be fed as much as they can eat until they are capped. The bee-milk fed to queens contains more sugar than that fed to workers and because it seems to have queen-making properties it is called royal jelly.
During this growth period queen larvae increase their weight by about 3,000 times and workers by 1,500. Such a rate necessitates five laval moults, four before capping, the fifth shortly after. Much of this increase in weight is as stored fats, carbohydrates and proteins, which are to be used in the next phase to convert the simple maggot-like larval body into that of the more complex adult insect with hopes and dreams and a lust for life.
Until the cell is capped the larval stomach is shut off from the intestines in other words it is a simple sac with no exit. Once the cell has been capped the larval stomach is plumbed in to the intestines and waste is evacuated via the anus into the inner end of the cell. The larva then spins the cocoon within which metamorphosis will take place, thus forming the propupa, but forming it inside the fifth and final larval skin (Snodgrass). The larva then moults for the last time but it does not shed the skin, instead it is retained as an outer cuticle within which, the body wall of the larva has already taken on the shape of the pupa. This stage is reached at 11 days in the worker, 10 in the queen and 14 in the drone (see Table 1.).
Between this and emergence are 10 action packed days, only 6 in the queen, with numerous big changes taking place. The progress of development can be followed through these days as in Hooper’s table by the colour of the pupa’s eyes, thorax or abdomen. Eventually the larva loses the maggoty shape as some of the 13 larval segments expand while others become constricted to differentiate the head and thorax from the abdomen of the adult insect. The adult head develops from the larva head, the first 3 segments become the neck and thorax and the last 10 become the abdomen although the first of these last ten is tightly constricted connector and strictly more a part of the thorax than the abdomen. According to Snodgrass – projections such as legs, wings and antennae are turned inside out early on. This suggests to me that the larva had them all along, but was wearing them on the inside, like inverted jumper sleeves.
When all the external changes have taken place the larval insides become broken down and digested to build adult organs. When all is complete the young adult splits the pupal shell, chews its way through the wax cell capping and emerges baffled and fluffy to potter clumsily about the brood nest until its cuticle stiffens and the hectic life of work engulfs it – unless it happens to be a drone.
Hooper,T. Guide to Bees and Honey. Blandford, London. 1991.
Snodgrass,R.E. The Anatomy of the Honey Bee. In The Hive and the Honey Bee. Ed. Dadant and Sons. Dadant Publications. Illinois. USA. 1979.
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