Becky Crew is a Sydney-based science communicator with a love for weird and wonderful animals. From strange behaviours and special adaptations to newly discovered species and the researchers who find them, her topics celebrate how alien yet relatable so many of the creatures that live amongst us can be.
IF YOU'VE never heard of 'hair pencils' before, feast your eyes on the bizarre Creatonotos gangis. This moth takes courtship so seriously, it spreads its pheromones using enormous, inflatable appendages that unfurl from deep inside its abdomen.
Found in the northern regions of Western Australia, the Northern Territory and Queensland, and all across South East Asia, this moth has evolved an ingenious way to find mates - even if they’re several kilometres away.
Hair pencils are highly specialised structures that can be found in many male butterflies and moths from the Lepidoptera insect group.
Also known as coremata (which means “feather dusters” in Greek), they’re used by the males to waft a heady cocktail of chemicals into the surrounding environment.
These chemicals have a dual function - when females are exposed, the chemicals act as both an aphrodisiac and tranquiliser, but when males of the same species get a whiff, they serve as a handy repellent to drive the competition away.
When a female approaches the male and likes what she sees (and smells), she will flick her antennae in response, and extend her abdomen towards him as a signal for him to commence copulation.
In the image above, you can see a Creatonotos gangis moth with his coremata fully extended, presumably triggered by a female in the area.
When males want to start wafting their pheromones around, their coremata are forced out of their abdomens using ‘sclerotised’ levers made from hardened cuticle.
While some moths and butterflies like this African monarch have fairly subtle coremata, C. gangis’ four-pronged ‘feather duster’ is a colossus.
Just look at that thing:
And here’s what these moths look like when they’re not trying to court a female:
(Image Credit: Credit: goldentakin/Wikimedia)
But the weirdness doesn’t end there, because the way these moths create their potent pheromone cocktail is just as mind-bending as their mode of transmission.
In its caterpillar form, C. gangis feeds on plants that produce pyrrolizidine alkaloids (PAs) – a bitter chemical that usually deters insects and other animals from eating the leaves.
It’s so reviled in nature that damaged plants will often increase their production of PAs as an extra precaution while they repair their leaves, and this can actually cause poisoning in unsuspecting sheep and cattle.
But somehow C. gangis evolved to love the taste of PAs, and during its caterpillar stage, the males consume enough PAs to produce pheromones by modifying the chemicals once they’ve been ingested.
They can also consume PAs as adults if they need a top-up, but if they don’t get enough during their lifetime, they won’t be able to grow coremata large enough to even be functional.
Of course, studying coremata is no easy task, because they’re usually tucked right up inside the male’s body. So Australian researchers from the CSIRO invented the aptly named ‘Phalloblaster’ – a device that inflates coremata in dead specimens.
As the researchers describe:
“The Phalloblaster inflates the genitalia with a stream of pressurised alcohol to create the same shape as when the insect was alive.
The alcohol dehydrates and hardens the structure, so that once the process is over, the genitalia remain inflated rather like miniature balloons. It makes them easier to study.”