Bee Biology and Castes

Bee biology studies the structure, development and roles of the queen, worker and drone that make up a honey bee (Apis mellifera) colony. A colony is not simply the sum of individual bees but a whole that lives together and makes decisions together. Almost every decision in beekeeping, from swarm prevention to queen rearing and from varroa control to wintering, rests on this biology.

What kind of community is a honey bee colony?

A honey bee colony usually contains a single queen, a number of worker bees that varies with the season, and drones only in spring and summer. At the summer peak a strong colony reaches tens of thousands of bees; it goes into winter with a much smaller population.

A single bee cannot live apart from the hive for long. The colony, on the other hand, regulates its temperature, stores food, defends itself, fights disease and reproduces by swarming. That is why biologists often describe the colony as a superorganism: the bees are the cells, the colony is the body.

There is no central control in the colony. Decisions emerge from the local responses of thousands of bees: foragers report sources by dancing, pheromones broadcast the state of the colony throughout the hive, and even a swarm's new home is chosen by a kind of vote among scout bees. That is also why the beekeeper intervenes not on individual bees but on the conditions affecting the colony: space, food, the state of the queen and health.

The colony's nest consists of combs built from beeswax. The layout is similar in almost every hive: brood in the middle, pollen (bee bread) around the brood, honey above and at the sides.

The three castes of the colony: queen, worker, drone

• Queen: The colony's only egg-laying female. She lays hundreds of eggs a day, over a thousand at the peak of the season, and holds the colony together with her pheromones.
• Worker bee: A female that normally does not reproduce. She does all the jobs, from cleaning and brood care to comb building and foraging.
• Drone: Develops from an unfertilised egg and has no sting. His only task is to mate with young queens from other colonies.

How do bees develop? Egg, larva and pupa

The honey bee undergoes complete metamorphosis: the egg, larva, pupa and adult stages are very different from each other. The egg hatches in three days; the larva grows fast, fed by nurse bees; after the cell is sealed with wax, the larva turns into a pupa and the pupa into an adult bee.

These durations are the beekeeper's calendar. When a queenless colony's new queen will emerge, queen rearing dates and the timing of drone brood removal are all calculated from these numbers. The fact that drone brood has the longest sealed period also explains why varroa prefers drone brood most.

Why do queens and workers turn out differently?

The queen and the worker come from the same fertilised egg; feeding makes the difference. A larva destined to be a queen is fed plentiful royal jelly throughout her larval life and grows in a special, vertically hanging queen cell. A worker larva, on the other hand, switches to a plainer diet after the first days.

This fact is the basis of queen rearing. A colony that becomes queenless can enlarge the cell of a young worker larva and make an emergency queen cell. The younger the larva, the better the queen; that is why a good queen cannot be reared from a larva older than three days.

The worker bee's tasks by age

A worker bee does different jobs depending on her age; this is determined by which of her glands are active at the time. The rough order is:

1. Cleaning cells (first days),
2. Brood care: the royal jelly glands in her head are at their most productive,
3. Comb building and nectar processing: the wax glands under her abdomen are active,
4. Guarding and ventilation,
5. Foraging: collecting nectar, pollen, water and resin (from about the third week onwards).

This order is not fixed; it flexes with the colony's needs. If there are few nurses, young bees stay nurses for longer; if foragers are lost, young bees go out foraging early.

The difference between summer bees and winter bees

A worker born during the season lives a few weeks; a winter bee reared in late summer and autumn lives for months and carries the colony through to spring. The difference comes from well-developed fat body tissue, which acts as a nutrient store and plays a role in immunity.

The Varroa destructor mite feeds mainly on this tissue and transmits viruses. If winter bees emerge from mite-infested brood they are short-lived, and the colony dwindles in mid-winter. This is why the mite load in late summer determines the winter.

How does the colony change through the year?

• Winter: The bees gather in a cluster, produce heat by shivering their flight muscles and eat their stored honey.
• Late winter and spring: Brood rearing starts, and with the first pollen and nectar the colony grows fast.
• Late spring: Drones are reared and the hive becomes congested; the colony turns towards reproducing by swarming.
• Summer: The main nectar flow; honey is stored, and the surplus is the beekeeper's harvest.
• Late summer and autumn: Egg laying decreases, winter bees are reared and drones are expelled from the hive.

How does this biology translate into beekeeping?

What is in this section?

The sub-pages cover the detailed biology of the queen, worker and drone, bee anatomy, bee races and climate adaptation. Each page explains the structure of the individual bee together with the work the beekeeper will do at the hive.