For a recent study published in Current Biology, Jurgen Heinze and Bartosz Walter from the University of Regensburg monitored the behaviour of over a hundred terminally ill ants. By observing 28 Temnothorax unifasciatus colonies containing individuals infected with Metarhizium anisopliae, a contageous, parasitic fungus, they found that these ants instinctively removed themselves from the nest to die in seclusion. As fungus pathogens can be easily spread through contact between infected and healthy individuals, Heinze and Walter suggest that this withdrawal from the colony could be evidence of an innate altruistic trait.
Having treated 70 worker ants with the deadly fungus spores, they recorded the behaviour of the 52 individuals that died within ten days of infection. The eight individuals who died with no evidence of spores notwithstanding, 70% of the infected individuals were observed to withdraw themselves from the nest before expiring. A further 21% were found dead outside the nest, but this happened overnight, so the researchers can’t be sure whether they left voluntarily or were actively removed. There were no observed instances of spore-treated ants being removed or attacked by healthy workers, however.
To refute the alternate theory that this behaviour is caused by pathogen host manipulation, as spores can be dispersed over a wider area when an infected individual ventures away from the nest, 70 uninfected individuals were exposed to 95% carbon dioxide to dramatically accelerate their aging. What Heinze and Walter observed in these moribund ants was the same tendency of social withdrawal prior to death, stating, “Actively leaving the nest and breaking off all social interactions thus occurred regardless of whether the individuals were infected or not.”
During the period leading up to their death, the infected and moribund ants weren’t treated any differently by the healthy workers. They would still engage in both active and passive interactions with their colony until it was time to leave. Once they left, the dying ants would never attempt to return to the nest.
Now while this might seem like an unusually selfless act, I’m willing to bet those dying ants won’t budge until they’ve milked every ounce of sympathy, gratitude, extra helpings of discarded milkshake and so on from the colony first. Or they’ll sulk like mad until they realise no one will miss them and then eventually clear off. But either way, it kind of renders any claim to altruism pretty much void in my books. Like, they’d all be happily marching towards some three-day-old chicken wing, playing whatever the new politically-correct name for Chinese Whispers is, “I have light bulbs made of dirt in my underpants and this email smells like a purple fax machine… LOL!!!!!1!” when one of them suddenly clutches his side all like, “Erm, you guys go ahead, I’ll just be a minute.”
“Dude, that’s not how you fix a stitch, you have to stretch your thorax, not scratch at it.”
“Oh, okay. Thanks…”
But the itching won’t go away, and no amount of, “What? Oh, no it’s really nothing, I just wore some old sweater to bed last night and forgot to use fabric softener so it was wicked itchy. Boy, did I learn my lesson! Guys?” will convince them that he’s not sick and pretty soon the expedition will come to a grinding halt.
“Look man, we all know you’re dying. It’s so obvious. But, you know, we didn’t want to say anything straight away, like, “Dead ant walking! Holy shit, move aside, this guy’s a goner!” because we’re not that heartless. Like, that time when you pretended to be tying your shoelaces when really you were scratching your gaster? We didn’t say anything. But come on, you’re not even wearing any shoes! Anyway, it really is time for you to, erm, “vacate the premises,” so to speak. For the team. You understand…”
And the infected ant will be all, “Oh okay. Fair enough. I don’t want you guys to, you know, die a slow and painful and itchy death like me. It’s cool, I’ll just go away and make a nest somewhere and perish. Alone. Oh, on second thoughts, I’ll probably be too sick and alone to make a nest for myself. I’ll just have to stand out in the cold and wait. For death. It’s supposed to rain tonight, right? That’s okay, I’m just going to die anywa—”
“Okay, sounds good.”
“What? That’s it? I bust my hump every day for this colony and–”
“Ugh. Fine. Does anyone here know this guy and want to say goodbye? Anyone? You there, dude with the big head, you know him?”
And some nervous-looking ant with a bulbous head will suddenly feel hundreds of compound eyes on him as he mutters in a very tiny voice, “What, me? Him? I don’t know, I don’t meet a lot of ants these days and the ones I do meet all look the same…”
Then another ant will pipe up, all like, “Hey weren’t you on that expedition last month where half the workers got stepped on by a labrador and you only got out of it alive because you were trapped in a huge protective bubble of saliva?”
And the infected ant will be like, “Yeah?”
“Thought so. Wait, what? No, no, guys, I don’t really know him. I just know of him. I’m not making a speech or anything, if that’s what you’re asking.”
So the colony will be like, “Well, we tried. We’d get Bighead over there to give you a hug or something, but then he’d probably get infected too, and we kinda need him to help carry that chicken wing back because it’ll probably be heavy. So. You know…”
“What about a brief applause then? Air-kisses? Can you at least bring me back some chicken before I head off? I’ll probably be too weak to find my own food pretty soon…”
“OH MY GOD NO AIR-KISSES JUST FUCKING GO.”
“Alright fine. I’m going. Bunch of ungrateful shits…”
“I heard that. Wow. Hate that guy. What an emo.”
“Hey can we get ice cream on the way to the chicken wing?”
“I don’t see why not!”
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