Reason One - Reproduction
Like all living things, honey bees have to reproduce or they will become an extinct species. I covered the mechanics of mating a few weeks ago, in this post. And last year, I posted about how chemistry determines the difference between worker bees and queens. Quick re-cap: if a female bee larva is fed royal jelly - which contains royalactin - for the 8 days after the egg hatches, then she becomes a queen, she is fertile, and she gets to mate. Otherwise, she becomes a worker, she's infertile, and sex is off the menu.
The thing about queen bees is that, apart from the mating flights (when they really don't want their more prudish sisters around) they don't travel alone. This means that, if a colony of bees is going to reproduce, there needs to be enough workers to divide into two groups - half the colony will stick with the old queen, while the other half will hang out with the new one. Also, there needs to be some drones around for the new queen to mate with, and hives don't start producing them until April. The size of the colony starts to expand in March, because the queen resumes laying eggs after taking a break over winter. The expansion continues through April, but here in the West Country it's only in early May that the colony will contain enough bees that it can split into two viable colonies.
So, once the colony is big enough to split into two, then the bees will need two queens - they already have one, of course, but they need to make another. So, they start work on making one. Firstly, they will make a "queen cup". This is a concave wax structure that faces downwards. As far as the queen is concerned, it's just another cell to lay an egg in, which she duly does (a fertilised egg, to be precise, i.e. female). Here's a photo of a slightly opened-up queen cup (with egg) that I took last year:
|An egg in a cup|
Once laid, the egg will hatch into a tiny larva, and the bees will start to feed it with royal jelly. As they do so, the larva grows, and the bees extend the cell downwards so that it is always a little larger than the larva. They continue to feed with royal jelly for 8 days, at which point they stop extending the cell and cap it off with wax at the bottom.
|A capped Queen Cell|
Then, something happens. Perhaps it's the last worker bee who finishes sealing the cell, or maybe a subtle chemical change in the hive. But somehow, something alerts the whole hive to the fact that there is a sealed queen cell. And then the bees start dancing. Not like the "waggle-dance", which is the one they use to tell their sisters about nectar-bearing flowers nearby. This is a mad, crazy dance, like a rave party - the hive is suddenly brimming with energy and the buzz raises in both pitch and volume. The bees start to nudge and harass the adult queen, until she has had enough and starts to warm up her wing muscles ready to fly. And then, no more than a minute later, one queen bee and 20,000 of her daughters take to the air - so many bees that the sky turns dark - in a magical co-ordinated aerial ballet that we call: A Swarm!
OK - if you're a non-beekeeper, you might not be thinking "magical". You may more likely be thinking "terrifying", actually. But swarms really aren't aggressive things - the bees are not at all in the mood for threatening anyone. They're just moving house. And after maybe an hour at most, they will settle on a nearby tree branch in a big cluster of bees. Later, anything up to a day later, they'll make the final journey to a nice big cavity in a tree, usually around 500 yards from the original hive, and start building honey comb in their new home.
So, the adult queen and half the bees have departed. The other half remain in the hive, with the new queen, which now starts to pupate. 8 days after she was sealed in her cell, the queen has finished metamorphosis and is now a fully-formed adult queen bee. She is now oriented head-downwards in the cell, and she neatly nibbles a hole in the bottom end of the cell, to emerge as the new ruler of her hive.
Reason Two - Managing The Succession
Failure to ensure an orderly succession from one monarch to another can be messy. Just ask the Plantagenets...
Not wishing to cause any such strife, bees have got quite good at making sure the transition from one queen to another is conducted in an orderly fashion. Death comes to all of us, and queen bees are no exception. The worker bees are able to sense when their queen is coming to the end of her productive life, mainly by detecting changes in the amount of pheromone that she produces. They will then start to build one or more queen cells. Usually this will be after the summer solstice. The timing here is interesting - if bees make a queen cell before the solstice, then they will generally swarm. If they make it after the solstice, they generally won't - instead there will be a managed succession known as supersedure.
There's good reason for this. If the bees start making a new queen before the solstice, then there will be enough time before winter for the swarm to establish itself, build wax and gather enough honey to survive until spring. After the solstice, time is very much against them, and a colony will normally be too small and under-resourced to survive the winter.
What I find really interesting is that bees have a very keen sense of time. They know when the days are getting longer, through spring. And they can detect when the calendar has passed the solstice, and the days have begun to get shorter. My bees were quite difficult to manage before the solstice, and I had to get very involved to prevent them swarming. Now that the days are already getting shorter, they have completely given up making queen cells.
So, back to supersedure. Usually there will not be many queen cells, often only two or three. And the worker bees will typically tear down all but one before the queens have finished pupating. Then, the new queen emerges, goes on her mating flights and returns to start laying eggs. So far, so normal. But there is one thing that is unusual about this arrangement - the old queen remains in the hive, and continues to lay alongside her daughter. Normally there is only one queen in the hive, but supersedure is the exception - the old queen and her daughter will co-rule the hive, often for several weeks. This arrangement will continue until the old queen dies - or, sometimes, is "assisted" to her mortal end by the workers. Bees can be both decisive and brutal, when they feel the need.
Reason Three - The Queen Is Dead
So, sometimes, things don't go according to plan. The queen might die unexpectedly, be killed by an incompetent beekeeper, or be assassinated by her own worker bees. So much for an orderly succession - it becomes paramount to raise a new queen, and soon.
Bees will normally detect that a queen is absent after around 12 hours. This, as with much hive business, is determined by pheromones - the workers will detect that the normal queen mandibular pheromone emitted by the queen is no longer present.
The apparent problem, at this point, is that there will not normally be any eggs laid in queen cells for the workers to grow into a queen. However, they can make use of a handy feature of brood feeding. As it happens, all worker larvae are fed royal jelly for the first three days, after which they are switched to the lower-fat, royalactin-lacking "brood food". So, as long as the colony has some larvae that are less than three days old, the bees can select two or three of them and decide to make them into queens.
How they choose the right ones is a mystery. What they do is not. Initially the larva will be in a normal, hexagon-shaped cell. The workers will nibble away at the bottom surface of the cell, and then extend it downwards to create the typical shape of a queen cell. Here are a couple of examples that I have photographed:
|Emergency queen cells|
This type of queen cell is referred to as an "emergency queen cell" (regular readers should be familiar with the pragmatic use of language among beekeepers!) The cell will often be shorter than a "swarm" or "supersedure" cell. However, inside the cell everything proceeds as with any other queen cell: the larva continues to be fed royal jelly, the cell will be capped after 8 days, and the queen larva will spend the next 8 days metamorphosing into an adult queen. Then, she will emerge, take her mating flights, and begin laying eggs, at which point order is restored. The emergency is over, and the colony resumes its everyday work of building wax, raising larvae, collecting pollen and making honey.