Thursday, May 23, 2019

Saturday, March 9, 2019

Bees and Stingers

Life is hard for pollinators. Well, life is hard for all creatures, not just animals but plants, too. They are all food for other creatures. Leave it to Jonathan Swift to put this concept in a nutshell. He tells us on Poetry, a Rhapsody

...every creature
      Lives in a state of war by nature...”

And explains further:

      “So, naturalists
observe, a flea
      Hath smaller
fleas that on him prey;
      And these have
smaller still to bit'em;
      And so proceed
ad infinitum.”

This is why every creature needs to invest on defenses in order to survive and to pass its genes to the next generation. This is also true of pollinators. We can use bees to illustrate this point, just as Jonathan Swift used fleas. They have a whole array of defenses, some of them we don't even know much about. So let us take a look at the better known one, the stinger.

Bees use their stingers in self defense and in defense of their brood. They don't use them for any other purpose. A stinger is located at the rear end of a bee. It is not like the sharp tongues or jaws of other insects like mosquitoes, horse flies or fleas. These insects use their piercing mouth parts for an entirely different purpose, primarily to obtain nutrition in the form of blood.

Ichneumonid wasps have an impressive appendage
at the rear end, but it isn't a stinger.
It is used only to lay eggs and it is called ovipositor

A stinger has a long and peculiar evolutionary history. Many millions of years ago there were wasps, ancestors of present day wasps and bees, which did not have stingers. They did have a long, pointy tube at the end of the abdomen which they used for laying eggs and got the name of ovipositor. Many wasps still use it for this only purpose. They inject an egg inside the body of another insect, for instance a fat, nutritious caterpillar. The wasp's baby grows surrounded by food and well protected inside the body of its victim. Ordinarily, it ends up killing its host. This is why they are considered something between a parasite and a predator and they are called parasitoids. Their victims are called hosts.

The hosts, in turn, developed defenses against their enemies. Many of the larvae hide themselves inside plant stems or under bark. So the wasps, had to come up with ways to overcome these defenses. Their ovipositors became stronger and longer. Other victims were able to fight back by squirming or biting their attackers back. So the wasps evolved substances that they could inject along with the egg. These substances paralyze the victim without killing it. Thus the progeny has fresh food at its disposal, rather than a decomposing corpse. And here is where the ovipositor took a curious turn.

In some insects it stopped being an ovipositor and became a syringe loaded with toxic stuff. Its function became purely defensive. The wasp found other means to lay her eggs bypassing the stinger. This happened many millions of years ago. All the descendants of those early wasps are what we know as stinging wasps and bees; ants also belong in this category. They all have a modified ovipositor which doesn't serve that purpose anymore.

The stinger took another turn. Bees don't attack prey. Their ancestors used to chase insects that were feeding on flowers. At some point, they discovered that flowers' pollen is so nutritious that it was preferable to feed this to their brood and not bother hunting animal food. In other words, they became vegetarians. However, they did not give up the stinger. They kept it for defense purposes. Obviously, only females have this weapon. Males never had an ovipositor and as a consequence they don't have a stinger either and can't sting you.

A bee's stinger is seldom seen.
It is tucked away at the rear end
One wonders why females have such a formidable defensive weapon while the males don't. The answer seems to be that males are shorter lived. Once they have mated there is no further use for them. The females, on the other hand have to raise a family. They need to defend the nest and the future generation, not just themselves.

I read recently that the budget for defense is bigger than all the other budgets put together, such as all the sciences, arts, education, the environment and so on. How is this possible? Later on, I thought that we are not all that different from the rest of the world, and I mean the entire living world, plants and animals, not just humans.