Fossil evidence tells us that insects have put wings to good use in their domination of the planet for the past 325 million years. However, some of these insects have given up their various motile flaps and flanges, yet still retained mastery of the airspace. That’s right – they ‘fly’ without wings.
Technically, ‘gliding’ ants don’t actually fly but, as their name suggests, they do glide – and with incredible aeronautical nuance, too. Quite a few ants do it, but the most studied species is Cephalotes atratus, a large black beauty of an ant, with the average worker measuring just over 1cm in length. It is found throughout the steamy lowland forests of tropical South America, and has evolved a clever way of addressing the challenges posed by its home habitat.
Where do gliding ants live?
The species lives in complex nests within the cavities and hollows of trees. It feeds primarily on the exudates produced by sap-sucking plant bugs found within the forest canopy, and also hunts down any other insects it can overpower. This wide-ranging, incessant search for food takes the ants up into the canopy then down to the forest floor, where they also scavenge.
Given that just one tree can represent a vertical walk of some 50m, you start to appreciate the scale of the day-to-day challenges these worker ants face.
What do gliding ants look like?
Cephalotes atratus is a striking minibeast. With a large, almost square head complete with spiky horns, it looks like a gothic demon. But that head is, in effect, a large aerofoil. Combined with flattened, blade-like leg segments, it gives the ant a high degree of aerodynamic control as it falls.
How do gliding ants move around?
Working in the rainforest canopy, scientists noticed that when the ants were swatted away, they didn’t fall to their inevitable doom, as would be expected. Instead, they somehow landed back on the same tree, just a few metres down from where they started, and scurried back.
In experiments, more than 90 per cent of tumbling ants could reorient themselves back towards the tree trunk from which they fell. They literally glide backwards. By holding their head and legs up and outwards, they do more than slow their descent: they can control their direction.
The ants use their eyes to orientate themselves towards the nearest pale surface – which, inevitably in the forest, is the bark of the tree from which they just fell. Sometimes, they come in too hard and fluff the landing, bouncing off the tree. Remarkably, they can recover, style it out, and initiate 180-degree turns to try again.
Such a mishap would represent a freefall to oblivion for most other wingless animals. But for something as light as an ant, hitting the forest floor is not a catastrophic event – it can survive the landing easily enough. The danger comes when an individual is separated from the chemical scent trails that its colony uses to navigate the complex forest structure, as it now has little chance of getting back to base.
No longer part of a massive formidable collective, the lost ant becomes exposed and vulnerable to predation – and if the forest is flooded, as many are for much of the year, then the list of sorry fates that might befall it gets even longer.
It turns out that many forest ants have evolved to glide to a greater or lesser extent. The evolutionary selection pressure is simply that if they lose contact with their tree, they’ll almost certainly die. So, anything that helps them to stay close to home is a significant advantage.
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Top image: a gliding ant or 'Cephalotes atratus'. Credit: Getty
