A worker honeybee is patrolling the hive. She walks around the colony watching her sisters clean cells, nurse brood, build comb and fan nectar. She sees drones being pushed aside by returning foragers impatient to unload heavy baskets of pollen. She turns as the queen walks past looking for suitable cells to lay eggs.
Such is the constant activity of the hive that it almost causes her to miss a haphazardly laid egg. Almost. She pauses. The egg lies lopsided along the wall of the cell, not neatly deposited at the bottom. The queen, a precise egg-layer, is never so careless, so the worker climbs in the cell to investigate. Every egg laid by the queen has a signature scent (pheromone) but this egg does not have her mother’s tag – it has been laid by one of her sisters, a rebellious laying worker.
The queen does not need to fear insurrection because her daughters are very efficient at policing themselves. Without hesitation, our worker eats her sister’s egg and if she happens to catch her sister laying more eggs, she will not treat her kindly.
My fourth winter study post discusses the social organisation of the honeybee colony as a well-structured and highly hierarchical community. My post is summarised and illustrated by beautiful infographics created for my blog by designer Keith Whitlock.
The social organisation of the honeybee colony including worker policing.
The honeybee is a eusocial insect, which describes an advanced level of social organisation. The most familiar examples of eusocial insects are bees, ants and wasps, which all belong to the insect order Hymenoptera.
Eusociality is demonstrated by:
- colony of overlapping generations from eggs and larvae to young and fully mature adults
- caste system that divides labour between reproductive individuals (queen) and sterile individuals (workers)
- responsibility for rearing young shared by large numbers of sterile individuals on behalf of the reproductives
The organisation of a honeybee colony revealing a eusocial society is given below:
Now that’s understood, here’s how the bees get organised inside the hive.
(diploid, fertile reproductive individual)
The queen is the most important bee in the colony. She lays eggs, providing a constant supply of new bees, and produces queen substance to control the workers and keep the colony working together as a cohesive whole.
The queen fulfils the role of egg-layer thanks to the royal jelly that she is continually fed in copious amounts as a young larva, thus ensuring she has fully developed ovaries and is able to mate. It is only the queen who can lay both fertilised eggs (which become female workers or potential new queens) and unfertilised eggs (which become male drones).
The queen mates not long after hatching and lays around 1,500 eggs per day; she may live between 3–5 years. She is not only a prolific egg-layer, she is also precise. With her long abdomen, she carefully deposits one egg, placed neatly in the centre, at the bottom of a cell (fertilised with a single sperm or left unfertilised) and marked by a pheromone so that the workers can recognise eggs laid by the queen.
The queen secretes a substance from her mandibular glands called queen substance – a heady mix of chemicals of which the main component is the pheromone 9-oxodec-2-enoic acid (9-ODA). The queen substance is constantly spread throughout the hive as workers lick the queen and then pass the chemicals to other bees. Queen substance, combined with a pheromone given off by her own brood, inhibits the development of the workers’ ovaries – effectively it acts as a natural contraceptive! It is quite effective as normally only 0.01% of workers can produce full-sized eggs and only 0.1% of drones in a hive are the sons of laying workers.
Queen substance modifies worker behaviour in other ways:
- inhibits building of new queen cells
- stimulates foraging activities for nectar and pollen
- encourages workers to build honeycomb
The pheromone 9-ODA is also released by the queen as a scent to attract male drones during her mating flight.
As the queen gets older her queen substance becomes weaker, and her egg-laying decreases, so that she has less control over her workers. They will eventually build queen cells to replace her.
Workers and worker policing
(diploid, infertile non-reproductive individual)
If you see a honeybee foraging on a flower in spring and summer she is likely to be a female worker. Almost every bee inside the hive is a worker and female.
Workers are the worker caste and carry out all the tasks for the colony. They live for around 40 days in spring and summer and between 5–6 months over autumn and winter.
Development of infertile females
After hatching, all young larvae are fed royal jelly for three days and then put on a diet of brood food, unless specially selected to become queens. Larvae who are continually fed royal jelly become queens with fully developed ovaries and are able to mate. Worker larvae are not fed royal jelly after day three of their development, have under-developed ovaries and are not able to mate. Their ovaries are unlikely to develop as adult bees due to the pheromones given off by the queen substance and the brood.
However, some workers may produce full-size eggs in their ovaries and become laying workers. Their progeny are destined to become drone because they cannot mate and have no sperm to fertilise their eggs.
Laying workers are quite careless. They may lay more than one egg per cell and because their abdomens are shorter than the queen’s the eggs are often laid haphazardly against the cell wall. They do not differentiate between worker-sized and drone-sized cells, laying drone eggs in worker-sized cells that hatch as drones with stunted growth.
Most importantly, worker-laid eggs are not marked by the queen’s pheromone, which helps other workers to police their illegal egg-laying activities. Worker-laid eggs are usually removed from cells and eaten by other workers (a practice known as oophagy).
(haploid, fertile reproductive individual)
Drones are the male bees of the colony and it is thought that their only role is to mate with virgin queens. A drone hatches from an unfertilised egg and inherits one set of chromosomes from his mother, the queen; for this reason, a queen cannot mate with drones from her own colony due to the risks of inbreeding.
Drones that mate with a virgin queen on her mating flight will die in the act, and drones that don’t mate but live to the end of the summer will eventually outlive their usefulness to the colony and be evicted by their sisters.
Drones do no work inside the hive, although beekeepers have observed in spring and summer that colonies with fewer drones can be bad tempered. Perhaps drones fulfil another purpose not yet discovered.
I’m looking forward to exploring the next item on the syllabus – dancing bees!
Visit my blog index for more winter study posts.
A great revision post from Emily Heath of Adventures in Beeland: 4th Honeybee behaviour revision post: social organisation of the colony
Mid Buck Beekeepers Association Blog’s excellent revision notes for BBKA module 6
Celia F Davis. The Honey Bee Inside Out. Bee Craft Ltd, ISBN-10: 0900147075
Ted Hooper. Guide to Bees and Honey. Northern Bee Books, ISBN-10: 1904846513