Opinion | No need to panic, the ants are on their way

When  a  Veromess or  pergandei  ant  gets  stuck  in  a  spider web, others rush  in to  the  rescue. They  dismantle  the  web  and  take  the  trapped  ant  back  to  the  nest

Among my most treasured possessions are two traps. That’s right: traps. I got them several years ago, when I spent time with some Phase (“phaas-ay") Pardhi families in rural Satara District, Maharashtra.

With many other tribes in this country, Phase Pardhis were once listed by the British, in their 1871 Criminal Tribes Act, as “criminals". When Independent India got rid of the Act in 1952, they were “denotified" — which is the term used to refer to them today.

The Marathi word “phaas" means “noose" or “trap", and that’s how this tribe gets its name. For Phase Pardhis catch small animals and birds with the traps they make. They are beautifully crafted, with short wooden pegs and nylon thread, and as beautifully rolled up into a compact bundle you can slip into your pocket. To use one, you stick the pegs in a line in the ground. Between each pair of pegs, the nylon thread forms a loop. When in place, you cannot see the pegs and you cannot see the loops. Neither can birds or rabbits that approach the trap. They walk into one of the loops and are firmly caught.

Beautifully crafted yes, but as my Phase Pardhi friend Gongajya explained all this to me one hot Satara afternoon, I couldn’t help feeling a twinge of pity for the hapless creatures caught in those traps. That afternoon came to my mind while I recently followed a short trail of scientific papers, and so learned what some other creatures do with traps.

The first paper is actually a report that appeared in National Geographic (“Gorilla Youngsters Seen Dismantling Poachers’ Traps — A First", July 18 2012) and it’s about mountain gorillas in Rwanda. These magnificent beasts live in Volcanoes National Park in that *country, a lush haven that’s under threat from Rwanda’s growing population. Just like Phase Pardhis do in Satara, hunters in Rwanda set simple noose-and-branch traps — thousands of them — in the Park. Their intent is to trap antelopes and other fleshy beasts for their meat. They are not interested in mountain gorillas, but every now and then, the devices catch one. They can cause the animal some serious damage.

In 2012, for example, an infant gorilla was trapped in one of these devices and tried hard to get free from it. As the article comments: “Adults are generally strong enough to free themselves. Youngsters aren’t always so lucky." As this one struggled, she wounded her leg and dislocated her shoulder. The rope from the trap cut deep into her leg wound and eventually gangrene set in. No surprise, she died.

Officials make regular passes through the park, locating and destroying these traps. On one such expedition soon after this infant gorilla died, they found and were about to demolish one particular trap when something amazing happened. Two young gorillas, one male and one female, ran towards the trap and destroyed it themselves. Then they ran to another trap nearby and destroyed that one as well. Clearly, they knew how much of a threat the traps posed. “The speed with which everything happened", the NatGeo report says, suggested that “this wasn’t the first time the young gorillas had outsmarted trappers."

It was, however, the first time that anyone had seen the gorillas behave in this remarkable way: identifying this mortal danger and getting rid of it. It wasn’t, however, the first time that anyone had seen other big apes behave like this with traps.

Three scientists at the Budongo Conservation Field Station in Uganda once reported how chimpanzees sometimes get their feet or hands caught in traps set by hunters (“Snare removal by a chimpanzee of the Sonso community, Budongo Forest (Uganda)", Stephen Amati et al, Pan Africa News, June 2008). This typically caused “subsequent loss of limbs or mutilation of hands and feet." But one afternoon in January 2008, the scientists were watching a pack of chimps make their way through the forest when a female chimp started screaming. Her right hand was caught in the nylon loop of a snare and she couldn’t move. The leader of the pack came over, took a look and broke the branch to which the loop was attached. Later, he used his teeth to actually cut through the nylon, totally freeing the female.

Then in 2010, two Japanese researchers reported “very few snare injuries" among chimpanzees in Bossou, Guinea (“Deactivation of snares by wild chimpanzees", Gaku Ohashi and Tetsuro Matsuzawa, Primates, January 2011). This was the case even though hunters set plenty of snares in those jungles, as they do elsewhere. Why so few injuries, then? They observed several chimpanzees “attempting to break and deactivate snares", and suggested “that such active responses to snares must be contributing to the rarity of injuries". It also seemed to them that this “behaviour has transmitted down the group" — meaning that ever-more chimps in Bossou are learning how to destroy these threatening traps.

Why write scientific papers and even a column in this space about such behaviour? Because what these gorillas and chimps did is so much like what we humans would do in such a situation. There is something inherently fascinating there — so fascinating that it’s hard to tear your eyes away. How do these ape species, so different from us in so many ways, learn to do these things that we humans would do?

And yet chimps and gorillas are also so similar to us in so many ways that, on reflection, maybe it isn’t such a surprise to see them behave this way. Maybe it would be more of a surprise if we saw other animals do such things. Like dogs. Or whales. Or giraffes.

Or ants.

Regular readers of this column will know that ants thoroughly enchant me: left-leaning ones, maimed ones, pheromone-doused ones and more. So when the paper trail about traps and chimps led me to some new research about ants, I was thrilled.

In particular, this is about a gleaming black ant named Veromessor pergandei that is found in the Mojave and Sonoran deserts of the American Southwest. These beauties harvest and eat grains, which is why they are described as “granivorous". A typical pergandei nest has a wide entrance surrounded by a low mound of soil, dug from underground, up to a foot in diameter. Around the soil is a huge pile of the discarded chaff from the grain the ants have consumed. Such nests are familiar and distinctive features of the desert landscape.

Now as far as I know there are no Phase Pardhis or African meat-hunters setting traps in the Mojave desert. Though of course, if such traps were there, it’s not exactly likely that pergandei ants will spring them and get caught. But Christina Kwapich and a colleague, from Arizona State University, have been studying these ants and found another kind of trap altogether that is, in fact, designed to catch them.

Thousands of pergandei fan out across the desert floor every morning to forage for grains.

A certain predator has learned to lay simple, but strong and sticky webs across their paths. This is the false widow spider, Steatoda nobilis. So a pergandei ant will be rushing along, minding her own business and searching for grain, and suddenly she’ll find herself entangled in a false widow’s web, with the spider somewhere nearby getting ready for brunch.

Just the usual, really. Predator and prey, the age-old equation of nature.

But Kwapich was startled to find that when an ant gets trapped in such a web, her pergandei siblings will rush to the rescue. They dismantle the web, take the trapped ant back to the nest and then groom her to remove any web remnants. What’s interesting is that the ants don’t seem to be able to even recognize spider silk. Instead, the trapped ant releases a chemical that spurs her mates to action. Kwapich confirmed this by plastering the same chemical on ant-sized inanimate objects: sure enough, other pergandei ants arrived to disentangle these faux-ants from the web.

To be sure, in this effort to rescue ensnared mates, a few of the rescuers — about 6% — are themselves lost to the spiders. But they still make the effort. Why?

To answer that, Kwapich and her colleague tried to estimate the costs and benefits of this behaviour. In their paper (“Destruction of spider webs and rescue of ensnared nestmates by a granivorous desert ant", The American Naturalist, May 7 2019), they concluded that if the false widows were left to their brunches, it would cost a typical pergandei nest 65,000 seeds a year. (Mathematics in the service of myrmecology: I love it). That’s a high price, and that’s what makes the attempt to rescue nest-mates worthwhile.

Like I said before, I treasure those two Phase Pardhi traps. But these days when I look at them, a vivid image sometimes comes to mind: a whole lot of ants, swarming all over a trapped gorilla. I think of him as Gulliver.

Once a computer scientist, Dilip D’Souza now lives in Mumbai and writes for his dinners. His Twitter handle is @DeathEndsFun

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