For my job, I routinely have people tell me “oh, I’m too old for this” or “I can’t do this, I’m going to just keel over right here”. We’ll be out on the trail for twenty minutes and already there are the groans and whines and the occasional curses. Sometimes, it’s even the actual elderly folks complaining about being on death’s door.
And after another solid experience with that today, someone claiming they were wholly incapable of walking another inch (they walked another two miles that day, in fact), I remembered something I’d read a long time ago.
Insects feel the same way.
Well, feel might be the wrong term. But they behave that way sometimes. They’ll look at the older folks within their group and try to decide how to best use them in and around the colony. Do you want to put your Auntie Ant in a nice Ant retirement home, safe from the ravages of the world? Perhaps you want to trust Grandma Ant to raise the next generation in her own image with her own words of wisdom?
In some Hymenopterans (some honeybees and ant species), there is a pretty firm answer.
They put ‘em to work.
There’s this thing called the Geometric Centrifugal Model of Work, which is a big and fancy sounding thing that breaks down pretty simple.
In essence, the older an individual member of the colony is, the further away from the colony’s center it will do its work. That means essentially the safest jobs are done by the youngest members of the colony, and the most dangerous jobs are done by the oldest members of the colony.
In this case, the safer jobs would be things like brood care or food processing, things that don’t really leave the nest at all. The more dangerous would be things like foraging and defense.
And when you think about it in an insect context, it makes sense. A lot of time, effort, and resources have been put into taking that individual ant from an egg into a full blown adult. And in some species, they can lose anywhere from 1-10% of the colony in a single day of foraging. Why would you risk hurting that investment before it has a chance to pay the colony back for its resources?
It’s kind of like buying a car. You take it out on the road the first few times and you’re pretty careful. You just made this investment, you want it to last. Maybe you put it into the garage every time a rainstorm is coming. After a few months you skip out on a rainstorm or two, a couple years later you don’t even bother putting it in the garage, and in another decade you’re donating it to a younger member of the family so they have something to beat the snot out of.
For some honeybees it’s a similar system. A typical European honeybee lives about sixty five to eighty days. The first twenty or so of those are spent as an egg, a larvae and a pupa. That’s pretty much when your car is being built in the first place, or when you’re saving up for the car.
From there they will emerge, and spend one or two weeks in brood care (babysitting, yuck) or queen care (still babysitting). After that, its food processing (converting nectar into honey, essentially) then a week or so late they become foragers or field bees. Finally, they will put that sixth foot into the grave and go to the great flower field in the sky.
The vast majority of those field bees will not die of old age. They’ll end up being eaten by something, injured by something, perhaps lost, or caught in some other natural phenomena.
So, long story short, the older you are, the further you go away, and the better chance you have of not making it back. Like a centrifuge, the individual is spun outward away from colony center until eventually they don’t come back.
And to wrap it all up with a nice little bow, it’s all chemically initiated and controlled (at least in bees). That means generally it’s not a big injury or something similar, which in some insects would be a death sentence and in others would just mean you go into retirement. It just happens for no visible reason. It’s almost like that car you just bought had somehow been manufactured to degrade. Like it was planned that this massive investment was to become obsolete.
Wouldn’t it be weird if that actually happened?
Hölldobler, B., Wilson, E. O., & Nelson, M. C. (2009). The superorganism: the beauty, elegance, and strangeness of insect societies. New York: W.W. Norton.