Deep in the subtropical rainforests of eastern Australia lives a rare caterpillar with a remarkable skull-like marking on its body that it brandishes to scare off predators.
The caterpillar in question represents one of the life stages of the southern pink underwing moth (Phyllodes imperialis smithersi)—a rare species found in a small number of locations on the country’s eastern coast in rainforests south of the city of Brisbane.
Different species of moths have evolved a variety of tactics to avoid predators. For example, caterpillars may blend into their surroundings using camouflage or hide under leaves. They may also have stinging hairs or accumulate plant toxins in their bodies in order to deter potential threats.
The southern pink underwing moth caterpillar, which grows to around 3 inches in length, uses camouflage to protect itself. At rest, the caterpillar looks remarkably like a dead leaf. But they also have threatening skull-like markings on the upper side of their thorax—the part of an animal’s body between its head and midsection—which they display when threatened or disturbed.
The caterpillar contracts to shorten its body, rears its head and thorax to display its markings, and also waves its rear segments. The “eyes” of the markings resemble those of a reptile predator.
So unusual is the appearance of the caterpillar when it displays these markings that some social media users on Reddit have compared it a baby Xenomorph—the fictional extraterrestrial species from the Alien movie franchise, a Halloween favorite.
“As the caterpillar grows it develops the skull pattern as a defence strategy to shock potential predators,” Mick Andren, a senior conservation officer with the Australian state of New South Wales, told Newsweek. “At rest the skull is not clearly visible, then when threatened, the caterpillar instantaneously snaps the skull at the predator by suddenly bending its body to reveal the full skull.”
Andren said this species has “excellent camouflage”—not only as a caterpillar but also once the moth has reached its mature stage.
When the caterpillar is young, its camouflage makes it appear like a young plant stem. As the caterpillar grows older, it looks more like a dead leaf. The forewings of the adult moths, meanwhile, look like brown leaves.
Aside from its camouflage capabilities, the moth also has other tricks to protect itself. The pink underwing of the adult moth that lends the species its name is also thought to be used as a defensive mechanism and is flashed suddenly when the moth is threatened, according to Andren.
Like other moths and butterflies, the southern pink underwing moth goes through several distinct life cycle stages, including egg, larva (known as caterpillar), pupa and adult.
The caterpillars feed on a plant known as Carronia multisepalea, which is a rare Australian subtropical vine that can grow very large, extending into the rainforest canopy. This food plant contains alkaloids that are poisonous to many other animals.
The plant species is thought to be essential for the caterpillars, thus the moth is only found where the vine grows.
The adult female moth is “exceptionally capable” of selecting the appropriate leaves on which to lay her eggs, Andren said.
The most appropriate ones are young leaves that are not too tough for the young caterpillar to eat and low down enough to provide protection from bright sun and wind.
The adult female also makes sure to lay the eggs on the underside of the leaf so that they are hidden from predators in the dark rainforest and in an area where there are enough leaves close by for the developing caterpillar to feast on. If all goes well, the eggs usually hatch after around eight days.
The caterpillars then feed on the leaves of the vine for about 18 days before forming a cocoon out of leaves in which they pupate for 25 days until they emerge as adult moths.
These adult moths, which can grow to relatively large sizes—the wingspan may reach around 5 inches—are thought to have a lifespan of around one month. During this time they feed on fruit, mate and the females find a suitable location to lay their eggs.
“They don’t have the hard mouthparts of many related, ‘fruit-piercing’ moths that are agricultural pests,” Andren said. “Instead they rely on the fruits getting damaged or starting to rot, so that they can suck food from them.”
It is likely that the adults are capable of flying significant distances, although this is inferred given that there is no data on this, according to Andren.
While the adult is relatively large, it is seldom seen. The Australian government listed the species as endangered in 2002. But more recent intensive surveys targeting the species have found more of the moths than expected, Andren said.
“While its true abundance is still unknown, it is more common than previously thought, he said.
The species is facing significant threats from habitat destruction. There are large tracts of rainforest remaining in the region where the moth lives, but a large proportion has been cleared.
“The moth is a rare species and it lives and breeds only in heavily shaded ‘old-growth’ subtropical rainforests,” retired CSIRO (Commonwealth Scientific and Industrial Research Organisation) entomologist Don Sands, who still actively researches many species, told Newsweek. “Populations have been severely fragmented by past clearing and logging.”
The species is also facing other threats, including fires that burn in the rainforests it calls home, which kill the vines and the moth itself.
“Within its range, the presence of the moth is a good indicator for remnant, undisturbed habitat and threatened ecosystems supporting other rare fauna and flora,” Sands said.