Frances Xu wrote to me:

Someone asked me why evolution lets a bee die after it stings.  I don’t seem to have a good theory. I have a bad one: it shows that bees are of a crazy type, so people are more afraid of them. Just wonder if you have any thoughts on this.

There are two ways to phrase the question.  First, why would a bee sacrifice its life to sting me.  Second, why would Nature design the bee so that it dies after it stings?   The answer to the second question is that after stinging the bee’s life is not worth living.  The answer to the first is that it wasn’t worth much before either.

The queen honeybee uses sperm stored from her maiden flight to fertilize and lay eggs.  Time seems to be the only binding constraint on how many bees she can bring to life.  There is no opportunity cost because her capacity is essentially unlimited.   This means that the marginal bee has close to zero net marginal value for the colony.

The marginal bee’s value at birth incorporates the value of stinging together with the value of all of the other services it contributes to the colony.  When the bee loses its stinger it loses its ability to sting and its value to the colony drops a discrete amount.  Now its value to the colony is negative.  The cost in terms of demand on colony resources for survival outweighs the benefits.

At this point it is optimal for the colony that the bee should die.

Now if the bee were genetically identical to the colony then its interests would align perfectly and it would therefore also be in the bee’s interest to die.  In fact the bee is genetically identical only to a component of the colony:  those other bees produced from the sperm of the same drone.  (Roughly 15 drones mate with the queen.)  Since the bee’s contribution to the colony is presumably shared by all bees, this means in fact that the bee has even less incentive to go on living.

The final variable is whether the bee could expect someday to mate with a new queen and get his genes into a new colony.  That prospect would give the bee reason to live.  But worker bees are sterile.

Drones are not.  And drones don’t die when they sting.  (update: drones don’t have stingers.)