Many animals have powers of perception that lie far beyond human comprehension. Take electroreception, the method by which sharks and rays scan for the electrical fields of their prey, or the magnetoreception that helps homing pigeons find their way. But, as mind-bending as these abilities are, I am almost more awestruck by those animals who rely on senses just like our own—smell, sight, taste, and so on—but do so through entirely different means.
Moths, for example, have a sense of taste. But they do not taste with their mouths. Moth taste buds are located on their feet, sampling everything they land on. In fact, most have taste receptors all over their bodies in the form of sensitive scales and bristles—like one enormous tongue.
And taste is not the only moth-sense that functions differently to our own. Some wear their eardrum on their abdomen: it is a simple membrane called a “tympanum,” which vibrates in response to the ultrasonic pulsing of bats. It is unlikely that they can distinguish between the different frequencies; for them there is no “high” or “low,” only “sound” or “no sound.” That’s all they need. As soon as they hear the threat of an oncoming, moth-munching bat, they escape by using evasive manoeuvres—jinking, darting, behaving erratically—and, in the case of hawkmoths and tigermoths, produce competing signals, jamming the bat’s sonar or even ingeniously mimicking the audio profile of a different variety of moth—one that happens to taste bitter.
Peppered moth caterpillars have the ability to absorb visual information through their skin, scanning their environment for colour and matching their bodies accordingly so as to escape the notice of predators. How do we know? Well, writing in the Communications Biology journal in 2019, researchers noted that the caterpillars could change colour—chameleon-like—to match black, white or lime-green sticks. But these remarkable camouflage skills seemed out of step with their incredibly rudimentary eyes (ocelli). As an experiment, the scientists “blindfolded” caterpillars by painting over these ocelli with black acrylic paint and found, to their amazement, that the caterpillars continued to change colour in concert with their backgrounds. DNA analysis later identified genes associated with sight expressed in the skin of all body parts.
Perhaps the most philosophically interesting question raised by the life of the moth is that of metamorphosis. The human lifecycle brings people through very different stages of being—but the difference pales beside the drama of the moth’s journey through existence, which divides into discrete chapters: larva, pupa, moth.
After hatching, moth caterpillars can take anything from a few weeks to a few months to reach full size; when they do, they will spin a silk casing called a cocoon around themselves and pupate. Inside the cocoon, a strange and unnerving process called “histolysis” takes place: enzymes are released that dissolve most of the caterpillar’s body, before this soup of proteins is reformed into its winged adult form.
It’s a lepidopterological twist on Theseus’ paradox: if, over the course of metamorphosis, every part of the caterpillar is melted down and reshaped, is it fundamentally the same being at the end of it? Is the creature that exits the pupa of one and the same mind as that which entered it?
The answer to that question is very difficult to know with any degree of certainty. But we do have some surprising findings that suggest that yes, it is. Back in 2008, researchers at Georgetown University taught the caterpillars of tobacco hornworm moths to associate the smell of ethyl acetate (nail polish remover) with electric shocks—and to avoid the smell wherever possible. When the scientists tested them as adult moths, they still had an aversion to the smell, indicating that they had retained the memory, or at least the association.
How much, exactly, do moths remember of their early, ugly-duckling years? Perhaps not much, but as I’ve blocked out most of mine too, I guess I can sympathise.
