Friday, October 30, 2020

Tales From The Ant World ~ A Respite From the Pandemic

When I was an elementary school aged child, I spent some time (a few weeks? months?) putting down bits of food for an ant colony whose scouts explored one corner of the floor of our bathroom.  It never took long for the morsels to be found and swarmed.  These were, I believe, the ant commonly and aptly (though unimaginatively) called “Little Black Ant.”  It bears the somewhat dismissive scientific name of Monomorium minimum.  The genus name reflects the monomorphic nature of these specific ants – workers come in only one type or caste.  The species name speaks for itself.

I recently finished E.O. Wilson’s latest book Tales From The Ant World (2020) and went in search of ants.  Surprisingly, they were scarce, perhaps because the weather, though relatively warm, was overcast and threatening or, much more likely, because I wasn’t patient enough in my questing.  I did spot a Chestnut Carpenter Ant (Camponotus castaneus) on the bark of a tulip poplar in a nearby park.

Still eager to watch ants at work, I reprised my childhood tactic (though outdoors this time) and put out small pieces of a raisin along the back edge of a front step where I’d seen trails of ants in the summer.  Less than a couple of hours later, an area that had been nearly devoid of ants now had them streaming along the step directly to the piece of raisin nearest to their colony.  The raisin was enshrouded in little black ants.  They were old friends, M. minimum.

I turned to my fossil collection where insects as a whole, much less ants, barely make an appearance, and, then, only in two small lozenge-shaped pieces of Myanmar (Burmese) amber, estimated to be 99 million years old (Late Cretaceous).  This paucity isn’t just a function of what I’ve been interested in, but also reflects the challenge of fossilizing these terrestrial creatures.  (I’ve acknowledged on this blog that this kind of amber comes to the paleontological world with real human and cultural costs for the people of Myanmar.  I do remain disturbed about having purchased these items, and I recognize that one might justifiably label me a hypocrite and complain that my concerns weren’t felt deeply enough to prevent this purchase.)

Here is the best image I can make of an ant specimen ensnared some 99 million years ago in one of my amber globules.  The quality of the photograph is due to the damage suffered by the specimen and to the limits of my photographic equipment.

I won’t hazard a guess as to the genus of this specimen.  Though I looked up images of all Mesozoic ant genera that myrmecologist Phillip Barden lists as having been found in Burmese amber, none seemed substantially similar.  (Fossil Ants (Hymenoptera:  Formicidae):  Ancient Diversity and the Rise of Modern Lineages, Myrmecological News, March 2017, table 1.)  For comparison images of these Cretaceous genera, I relied on AntWeb hosted by the California Academy of Sciences.

In Tales From The Ant World, a slender volume (my e-version of the book comes in at 230 pages), Wilson tells stories about the strange and marvelous life of ants.  His book offers a welcome respite from the dread that plagues the human world at the moment.  In prose both informal and graceful, Wilson regales the reader with first hand accounts of the ant world.  [Later edit:  Thinking that Wilson needed no introduction, I failed to provide one.  I trust it suffices to say that he is one of the world's foremost myrmecologists (scientists who study ants), and has had an important and amazingly productive career.]

An early chapter offers an autobiographical account of being enraptured by ants in his youth (this portion is reminiscent of parts of an earlier autobiographical work titled Naturalist (1994)).  The bulk of the chapters treat different aspects of the world of ants through vivid accounts of Wilson’s work with these insects and the insights he’s gained from a lifetime of studying them.  In each of these brief chapters, Wilson tells engaging and often exciting war stories in an informal voice, yet each of these carefully crafted tales comes with a deliberate context and a scientific point or more to be made.  Superb natural history writing, indeed.

According to Wilson, ants inhabit an alien world, dominated by three foundational guidelines:  there is “absolute female rule,” many “eat their dead – and their injured,” and they “are the most warlike of all animals.”  All three of these precepts come together in a critical aspect of the life of a worker ant.  Workers are all female and, as they age, their tasks in support of the colony change and become decidedly more perilous.  Wilson writes, 

In a nutshell and put more plainly, where humans send their young adults into battle, ants send their old ladies.

He makes clear the underlying evolutionary impulse behind this phenomenon.

For ants, service to the colony is everything.  As individual workers approach natural death, it benefits the colony more for the old to spend their last days in dangerous occupations.  The Darwinian logic is clear:  for the colony, the aged have little to offer and are dispensable.

Natural selection works not only at the level of the gene in the individual ant, but also at the level of the colony as colonies of the same and different species compete with one another to survive.

Ant death offers Wilson the opportunity to recount the tale of how he figured out how ants recognize that a nestmate has expired.  First, one must understand that ants communicate through smell and taste; theirs is a world of chemical discourse.  The little black ants on my front step were following the scent laid down by a scout who first discovered the pieces of raisin.  She headed as directly as possible back to the nest, chemically marking her path.  The odors that make up and drive the ant world extend to scents that are unique to each ant colony, providing the means of identifying who belongs and who does not (the latter at risk of quick death).  Wilson describes how ants that die a natural death or of disease inside the nest are picked up by another ant and carried outside of the nest or to a pile of refuse in a separate nest chamber.  When first studying this process, he assumed this social behavior – the removal of the dead – was prompted by some chemical scent and so went in search of the triggering substance.  And a funny (though not without its morbid side) tale ensues.  Out of the bodies of dead ants, Wilson made an essence of dead ant which he painted on little wooden dummy workers.  Sure enough, other workers dutifully removed the fake dead.  He assayed the dead ant scent and determined what in it triggered the living workers’ response.  Using just that, he elicited the same behavior with the dummy ants.  Clearly a moment of joy as he notes, “There is no procedure more pleasing to a biologist than an experiment that works.”

But, he took things a step further, wondering what would happen if a living – that is, a moving, active – worker were painted with this substance.

The result was gratifying.  Worker ants that met their daubed nestmates picked them up, carried them alive and kicking to the cemetery, dropped them there, and left.  The behavior of the undertaker was relatively calm, even casual.  The dead belong with the dead.

Until these living, though dead-smelling, ants managed to rid themselves of the death scent, they were repeatedly returned to the charnel house by their nestmates.

Wilson, like all good raconteurs, often frames his stories around the extremes, for instance, the accounts of the gentlest and the most vicious ants in the world.  In making his case for such labels, he capitalizes on our hunger for the unusual and propensity for treating everything as a “horse race,” while drawing us deeper into the ant world.  Gentlest and most vicious?  For the former, he describes the Dolichoderus imitator as the “most timid” ant “with none of the warrior spirit we usually associate with ants.”  The D. imitator is small and lives in sparsely populated colonies, nesting in decaying leaf detritus in the Amazon.  Disturb the nest and the workers will quickly grab a larva or pupa and speed away, seemingly in random directions.  As Wilson observes, “Ant colonies possess superb resiliency.  Timidity pays off in the rain forest, if you can run fast.”

As for the most aggressive species, Wilson first poses the question of why there might be a range in behavior from “pacifist to warmonger” and explores the answer to the question by considering some candidate species.  In so doing, he illustrates an evolutionary principle:

The more defensible the nest site and the more valuable the resources it contains, the more powerful the defense and the greater the fierceness with which it is applied.   In short, ants are as mean as they have to be in order to protect their home.  No more, no less.  (Italics in original.)

The label “most vicious” is won, in Wilson’s experience, by the Amazonian species Camponotus femoratus which build nests that incorporate plants that grow on tree trunks and in the tree canopy.  In these nests, the ants create gardens for scale insects and mealybugs which dine on sap they draw from the plants and which also provide their ant hosts with nutritionally rich excrement.  As a result of the defensible nature of this nest and the importance of its contents, the C. femoratus are generally held to have “a frightening degree of ferocity.”  I would note that the Chestnut Carpenter Ant pictured at the outset of this post is a much removed cousin of the C. femoratus.

Wilson addresses the relationship of the ants of the Cretaceous, such as the one pictured earlier, with modern ants.  There seems to have been no “straight line” evolution from the Cretaceous ants, the so-called stem-group ants, to the modern ants (crown-group) that surround us now.  As myrmecologists Phillip Barden and David A. Grimaldi note, the fossil record for ants has a very conspicuous roughly 15-to-20-million-year gap that straddles the boundary between the Cretaceous and the Paleogene.  (Adaptive Radiation in Socially Advanced Stem-Group Ants From the Cretaceous, Current Biology, February 22, 2016.)  They conclude that the stem-group ant taxa we have so far found in Cretaceous material failed to make it through that gap.

Woven through these stories is Wilson’s important cautionary note that, though ant societies may have some aspects that we think resemble those of human society, the

real differences between ants and men are profound.  Ants create civilizations by instinct – because they are capable of doing nothing other than what they evolved to create.  For their part, human beings are torn by the competing needs of self, family, and tribe.  We use culture to banish instinct or at least tame it, even while using it to create our values.

This is true, yet distinguishing what ants do from what humans do, regardless of the genesis of the action, can be challenging.  The distinctions can be complex.  Consider the treatment of the elderly.  As I quoted Wilson earlier, as worker ants age their jobs change, becoming riskier.  They are, he notes, following the evolutionary dictum that “the aged have little to offer and are dispensable.”  No retirement, no resting on one’s laurels, rather, going forward into danger for the good of the colony.

Human society is quite different in its attitude toward its senior citizens.  Or is it?  In the midst of the pandemic, some malevolent (revealing my attitude) voices have posited that the elderly, having lived a long life, should be prepared to be sacrificed on the altar of the “return to normal,” to the reopening of the economy and society.  I mean, so the logic goes, seniors have nothing to offer, particularly in comparison to the young, and they should do the right thing and serve the greater good.

I reject that position (and not just because I’m a senior myself).  Wilson offers one wonderful example of why.  I love the tale he tells of the swift “sprinter” species of ant that can be found in Mozambique.  He writes of traveling around that country partly by helicopter studying and collecting different kinds of ants to be taken back to Harvard for its collections.  While searching an inland forest, he found a nest of Ocymyrmex ants which are able to accelerate quickly.  Wilson, working in the blistering heat of a noonday sun (a phrase involving “mad dogs and Englishmen” comes to mind), tried repeatedly to capture some of these speedy workers.  The effort was prolonged and taxing, but ultimately somewhat successful.  The year of this tale was 2015; at the time, Wilson was 86 years old.

[Later addendum:  Upon reflection, I've decided to make it abundantly clear:  this book itself is powerful evidence to wield against those who would cavalierly countenance sacrificing the aged.]

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