Key points
- Australia has over 22,000 species of moths, but only about 10,500 have been named.
- Moths are the dominant night-active insect group.
- They're pollinators, recyclers, pests and plastic eaters.
Moths are often overlooked. Their close relatives, the butterflies, steal the scene with their daytime showiness.
But there are many more moth species than butterflies, and they have many different lifestyle strategies. Their caterpillars generally feed on plants, which makes some of them, such as the Fall Armyworm, a serious pest for crops.
A few of our favourite wings
Dr Marianne Horak AO is an Honorary Fellow in Lepidoptera at the Australian National Insect Collection (ANIC).
She worked mainly on tortricid and phycitine moths. These include fruit pests such as light brown apple moth, codling moth and macadamia nut borer, and on our iconic scribbly moths.
In Australia oecophorid moths, also known as Mallee Moths, are the biologically most important group. In other countries, there are only a few hundred of these types of moths. However, in Australia we have 5,000 species!
“These moths are really important in the Australian ecosystem as they do the heavy lifting on recycling leaf litter from eucalyptus and other myrtaceous trees,” Marianne said.
Some larvae start eating leaves on branches and then detach them and parachute to the ground. Other species eat leaves already on the forest floor.
“If caterpillars eat live leaves then they have to deal with the plant’s defences. Their life hack is to detach the leaf so they can extract the nutrients from the drying leaf more easily.”
An unbeleafably good idea
These crafty caterpillars have cracked the code on how to access a massive food resource in Australia’s dry environment.
“In wetter climates, dead leaves are usually decomposed by earthworms and fungi,” Marianne said.
“In Australia our eucalypt forest leaf litter is generally drier and earthworms and fungi can’t process this easily."
So, these caterpillars are the essential initial decomposers of eucalypt leaves.
“In eucalypt plantations overseas where these moths aren’t present, eucalypt leaf litter can build up to big volumes as it’s not being recycled by these committed caterpillars,” she said.
The caterpillars feed mainly in the cooler seasons. In summer, they move deeper into the litter to survive dry periods.
“It means these caterpillars are vulnerable to wholesale controlled burning of large areas in the winter months,” she said.
“Mosaic burns, where patches remain unburnt, mean they can survive in remnant areas. They then repopulate the burnt areas where a lot of leaf litter is often available after fire.”
This often-overlooked group of moths has been fast evolving as Australia has become drier. It now makes up 20 per cent of Australia’s moth species.
“The oecophorid caterpillars occupy very specific niches, and they’ll continue to evolve as the climate changes," she said.
Hit me with your best moth
The wings of Lepidoptera are covered with minute, overlapping scales, which give them their often-colourful camouflage patterns. These scales also keep them warm so they can be active at night.
“Moths evolved scales which became a warm coat to insulate against losing the heat from the flight muscles. This allowed them to become nocturnal. It’s a better survival strategy as there are fewer predators at nighttime,” Marianne said.
Don’t moth me now: Fall Armyworm
The menacing moth Fall Armyworm (Spodoptera frugiperda) is a global plant pest.
The adult moths have been known to migrate in masses and the caterpillars can destroy large areas of food crops in a short period. In Africa up to 17.7 million tonnes of maize annually is lost to fall armyworm.
Our researcher Dr Wee Tek Tay and his Pest Genomics Team used next generation sequencing techniques to analyse the genetic diversity of this pest.
“We found genomic evidence to suggest that this moth was introduced multiple times globally, including in Asia, from its home range in the Americas. Subsequent multi-directional spread enabled this species to dominate the agricultural landscape across its new invasive ranges in Africa, Asia and Australia,” Tek said.
“And we found the Australian populations had big genetic differences across Queensland, the Northern Territory and Western Australia,” he said.
This suggests the moths came from separate places and different populations, rather than just spreading from a single introduction point.
"We have detected different pesticide resistance profiles in the Western Australian and Queensland populations," Tek said.
“We’ll need to monitor gene flow into and between different populations in Australia to manage any increased insecticide resistance and develop management strategies.”
Eating plastic for breakfast
Another moth with a unique superpower is the Greater Wax Moth (Galleria mellonella).
In the wild, their larvae feed on beeswax, so beekeepers consider them a pest. But in 2017, an accidental discovery uncovered their hidden potential. Scientist and amateur beekeeper Federica Bertocchini left some larvae in a plastic bag after cleaning her hive. When she returned later, she saw they had eaten their way through.
That's how scientists discovered the Greater Wax Moth larvae have a superpower. They can break down common plastics! Specifically, their saliva and gut microbiota can degrade polyethylene, polystyrene and polypropylene.
Recently, our researchers released an improved genome sequence of the Greater Wax Moth. This will help shed new light on their plastic-eating abilities. With further research, these grubs could help unlock a bio-based solution to plastic waste.