About... Drones

Science warning:  this post contains actual science.  You have been warned...

Adult themes:  this post contains stuff about sex.  If you're a teenage boy, this will be considerably less exciting than it sounds...

Bees are male and female.  But whenever you see a honey bee, it will almost certainly be a worker bee, and they are all female.  Also, they are sort-of infertile (but not completely, as I'll explain later).

Drones are the males.  And they are most definitely not workers - in fact they don't forage, and don't do any work inside the hive.  They are so lazy that they expect the (female) worker bees to feed them.  In fact, they really only have one purpose - sexy time with a queen bee.

Before we get onto that, it's worth looking at the physiology (and a bit of biology) of the drone.  Firstly, a picture:

They're a little larger than worker bees, and the abdomen is rounder at the end.  This is because they don't have a sting.  Drones also have a larger thorax, to accommodate bigger wing muscles.  Although drones are lazy, they need to be powerful and fast flyers.

The other notable characteristic is a drone's eyes - they are much bigger than a worker bee's eyes, and cover almost the whole head.

So, why the differences?  Since a drone's only job is to try to mate with a queen, he needs to make sure he's good at it.  Drones will first locate a queen by the pheromones she emits.  He then needs to get to her as quickly as possible, as there will be other drones competing with him.  So - bigger wing muscles mean more speed.  Once the queen is in visible range, he uses his visual acuity to make the final approach - hence the big eyes.

But why no sting?  The tip of his abdomen, where the worker bees have their sting, is used for something else on a drone.  It's his bee boy bits.  y'know - his willy.  Actually the proper name for it is an "endophallus".  But it's still his willy, really.

The actual mating act is fairly brief - only a few seconds.  After which the drone departs.  Leaving his willy still stuck inside the queen!!!  Yep - it snaps off.  And, in case you're wondering - yes, that is fatal.  Does he die happy?  one can only hope...

Here's a picture of the underside of a (sadly deceased) drone.  The orange "blob" you can see is the remains of where his endophallus was torn out while mating:

So, that's the physiology.  The genetics are quite fun (you did read the science warning, didn't you?)  If you paid attention in biology class, you'll remember that humans have two sets of chromosomes - one set from their mother, and one set from their father.  And humans are female if they have two X chromosomes (XX), and male if they have an X and a Y (XY).

Bees are different.  Female bees (i.e. workers and queens) still have two sets of chromosomes - a maternal set and a paternal set.  But drones only have one set of chromosomes, all from their mother.  Weirdly, this means than male bees have no father.

This all happens as a consequence of the way fertilisation is done.  When a (poor, doomed) drone mates with a queen, he doesn't fertilise her eggs straight away.  Rather, his sperm is kept inside a special organ in her abdomen (called the spermathecal gland).  Then, each time she lays an egg, one sperm is released from the spermathecal gland to fertilise it - but only if it's to become a female worker.  It's possible for the queen to lay an egg and not release a sperm - in which case the egg will develop into a male drone.

The mechanism for producing fertilised (female) or unfertilised (male) eggs is interesting, because it's under the control of the workers.  Typically, they will make cells in the wax comb that are 5.2mm across.  When the queen lays the egg, her back legs will be on either side of the cell, so they will also be 5.2mm apart.  This particular distance triggers a reflex which releases the sperm.

If however, the workers make the cells slightly larger - around 6.5mm across - then the queen's legs are further apart.  Actually, they are too far apart to trigger the sperm reflex, so when she lays the egg, a sperm isn't released.  The unfertilised egg will have only one set of chromosomes - from the queen.  But in the weird world of bee sex, an unfertilised egg will still develop - it grows up to become a male drone.

I mentioned earlier that (female) worker bees are sort-of, but not completely infertile.  They're not capable of mating, as their "lady parts" aren't fully developed.  And normally they don't lay eggs - partly because the instinct to do so is suppressed by hormones that the queen produces.  However, they are capable of producing eggs, and every so often a worker bee will lay an egg.  These are normally dealt with fairly quickly, because there are worker bees who have the job of tidying up any stray eggs that have been laid by their sister workers.

However, in a hive which has lost its queen, and which also doesn't contain any developing queen cells, things get strange.  The hormone to suppress the laying instinct in workers is absent (because there's no queen to produce it).  So, worker bees start laying eggs - and more than can be tidied up.  Now, remember that none of these workers are capable of mating, so these are all unfertilised eggs.  So, they all develop into drones.  The hive is now in trouble - it's incapable of producing new workers, and instead is creating increasing numbers of drones.  Who will do the work in the hive?  The answer is - after around 6 weeks - nobody, because there will be no workers left.  The hive is doomed.

So, why does evolution allow such a suicidal mechanism to occur?  The drones are the answer.  Once the queen is lost, the hive can't produce workers so it is doomed anyway.  But the mass production of drones in the final few weeks means that the hive has increased its chances of its own bees mating with queens from nearby hives.  Even though these particular bees can't carry on, they can still propagate their genes to other hives, and those genes will build the future workers and drones of those neighbouring colonies.  Life finds a way!