When I first set eyes on a male Australian horror moth, I had to do a double-take. What on Earth was I looking at? Was this a practical joke, or some sort of poorly constructed chimera?
It looked as if it was made from bits of different insects stuck together with glue. Parts of its anatomy registered as familiar – it had eyes and antennae, six legs, wings and other mothy things, but all of that was upstaged by, well… I don’t know what.
The male Australian horror moth (Creatonotus gangis) is also known as the Baphomet moth, after the multi-horned occult deity (whether it deserves such fear-inducing names, I’m not sure). For most of its life, it looks like a regular moth, albeit larger than average, with a 4cm or so wingspan.
Those familiar with their moths might even recognise it as a member of the boldly patterned tiger moth family. It is decorated with patterns and panels of contrasting colour – pale brown wings with dark patches, yellow legs with black socks and an outrageous scarlet abdomen spotted with black. What dangles from its rear end needs some explaining, though.
From the tip of its abdomen it extends four long, shiny, grey and fluffy organs known as coremata (which appropriately translates as ‘feather dusters’ in Greek). In some males, the coremata are longer and larger than the moth itself.
Such accessories must have a purpose, and clearly the one thing they can’t possibly do is help with the everyday tasks of being a moth. For a start, these floppy, fuzzy fingers would be aerodynamically compromising. They’d surely make the moth sluggish and indeed vulnerable.
Luckily, nature has thought of that and has designed the coremata to be eversible and inflatable. During regular business hours, they are flat-packed away inside the male’s abdomen, allowing him to wing his way in search of a mate. When he detects a female in close range, he fills his secret weapon with blood and air, and then, as if blowing up a strange party balloon, unfurls these ludicrous-looking organs. As they reach full turgidity, a covering of lustrous fluff stands erect.
The purpose of these undoubtedly spectacular appendages relates to surface area and sex. The bigger your coremata, the more luck you’ll have with the ladies. It’s as simple as that.
It’s in those long filaments of fluff that the courtship magic happens. Known as hair pencils, they are covered in glands that produce a pheromone called hydroxydanaidal. Hair pencils increase a male’s surface area, enabling him to disperse and waft this chemical more effectively and, as a result, he’s more likely to attract a mate.
A healthy male can produce 400 micrograms of his aphrodisiacal scent, and it seems that the pheromone is directly influenced by the quality of the moth’s diet as a caterpillar. If he was eating a plant rich in alkaloids, then he would produce more hydroxydanaidal and therefore bigger coremata to distribute it. This form of sexual selection can lead to coremata that are right at the limit of what a male moth can pack into his abdomen.
The pheromone does not only serve to attract females. It has another, slightly less honourable function as a tranquilliser. In the presence of big males, females become overwhelmed by the scent and are easier conquests. An added benefit is that while irresistible to the females, the strong pong is a deterrent to rival males. Presumably, they too can judge the scale of the competition by the strength of their pheromone and are sent packing.
Illustration by Peter David Scott/The Art Agency
