In this COVID era, nighttime entertainment often comes down to watching one of the plethora of programs offered by streaming services. Let me make a recommendation. Summer is a time for ants to romp around, much to the annoyance of many people. Not me. I like ants, they are great little chemists. That’s why I’m suggesting Disney Pixar's “A Bug’s Life”. It is a lot of fun and we can even make it educational. The film is an epic tale of an ant colony terrorized by grasshoppers, essentially a struggle between good and evil, but along the way we manage to learn something about the amazing world of ants. There is intriguing science hidden in the whimsy.
The film opens with a long line of ants, marching in single file, carrying bits of food back to the colony. All of a sudden, a leaf falls and blocks the path. The ants behind the barrier go into a state of panic, they don’t know which way to turn. Believe it or not, this engaging little scene is based on real ant behaviour. Over 4,500 species of ants have been documented in the world and many of these use specific chemicals, known as trail pheromones, to guide their mates to food. Leafcutter ants, (Atta texana) the heroes of the movie, are a prime example.
These guys are leafcutters, to be sure. Their queen-to-be is called Princess Atta, and Flik, the eventual savior of the colony, is constantly devising ingenious machinery to cut leaves. Real leafcutter ants collect food by using a trail marking chemical. Workers go forth and mark the route to food with a chemical secretion. Other ants pick up this scent and dutifully march, one behind the other, to gather the goodies and transport them back to the nest.
The ants’ sensitivity to the pheromone is incredible. Just one milligram of the leafcutter scent is enough to lead an army of ants around the world three times. Careful observation of ant behaviour has revealed that receptors on both antennae are necessary for efficient trail following. The insects actually follow a zig-zag path, repeatedly crossing the trail of scent. They bob their heads side to side, searching for the marker chemical, turning back towards the path when one of the antennae passes out of the vapour trail. If the antennae are crossed and then glued in place, the ants get disoriented. Similarly, a physical barrier along the path leads to great confusion, just like in the movie.
Trail pheromones are understandably species-specific. Why should food discovered by one type of ant provide a meal for members of a different colony? Leafcutter ants and fire ants, for example, use completely different chemicals to mark the path to food. Just like “leafcutter,” the term “fire ant" is very appropriate. It refers to the sensation a victim gets when bitten by these bugs. Fire ants use a very efficient chemical weapon, formic acid, to protect themselves in the face of danger. “Formic” derives from the Latin formica, meaning ant, and the acid was actually first isolated from the little creatures in the 17th century by crushing them in a mortar.
Fire ants tend to be quite aggressive. Ogden Nash reflected on this when he poetically mused: “Would you be calm and placid if you were full of formic acid? Probably not. The pain of a formic acid sting is the gist behind a unique coming-of-age ritual in some South American native tribes. The candidate thrusts his hands into a bag filled with fire ants and if he is able to withstand the pain without withdrawing his hands, he is judged to be ready for marriage. There is a joke in there somewhere, which I will leave to fledgling comedians with unhappy marriages.
About 10% of the world’s ant population produces formic acid, some of which finds its way into the air. Would you believe that this can be a significant source of acid rain? A single ant of course releases an insignificant amount of formic acid, but multiply this by 100 trillion and you can account for about 25% of the acid rain in the Amazon! And this is no longer only a South American concern. Fire ants were introduced accidentally into North America in the 1930s and now infest about a million hectares, taking a big bite out of food production. They travel in huge colonies and will attack at the slightest provocation, sometimes even stinging pigs and chickens to death. Still, fire ants are nothing like the meat-eating driver ants of the African jungle which have been known to reduce a cow to bare bones in a couple of hours. You want to stay out of the way of those fellows. But there are no worries when you sit on your couch and watch “A Bug’s Life.”