Flystrike starts in the greasy folds of skin that characterise Merino sheep. Moist and lined with lanolin, it's the perfect spot for blowflies to lay their eggs. The maggots hatch in the darkness and feed on the living tissue of sheep until they emerge, sheltering in wet lumps of wool, marked by large wounds with weeping lesions, swollen skin and the smell of rotting flesh.
One blowfly can produce up to 300 eggs per cycle, laying a new batch every few days. Without rapid, intensive antibiotic treatment, the sheep will die.
Craig Smith, a sheep contractor in Grenfell in the New South Wales central west, has seen his fair share of flystruck sheep over the past 20 years.
"It's pretty horrific, to have maggots and being eaten alive," he says. "Then there's blood poisoning and everything else that goes with it."
It is distressing for the sheep and confronting to watch. Animal rights groups have campaigned against mulesing for decades, and many wool buyers, including retailers from Country Road to Big W, will no longer buy wool from sheep that have been mulesed.
Pain relief is only required by law in Victoria and Tasmania, with other states and territories requiring some treatments for sheep of certain ages. Topical anaesthetic and antiseptic laced with adrenaline is often used to reduce bleeding.
The procedure causes the open wound to form tight scars and smooth skin; no folds for maggots to hide in and no wool to provide shelter for flies in the animal's most vulnerable areas. Smith says it's a price worth paying.
"Nobody likes mulesing, I don't even like it," he says. "But at least you know you're doing a good job and getting the right result. We are doing it for the benefit of the sheep."
Cowra sheep farmer Doug Wright has worked with non-mulesed sheep for two decades, using selective breeding to develop sheep with soft, rolling skin instead of the fatty wrinkles typically seen on a Merino. Wright says his sheep haven't needed to be jetted - a chemical spray process that coat sheep in insecticide - and have avoided flystrike.
"I'm looking for thin, loose, skins that were producing fast-growing wool," he says. "It means the wrinkle was taken off the sheep, and meant the place for flies to live and lay eggs was eliminated."
The downside is a reduction in fleece value but Wright says the lower cost of running healthier sheep makes up the difference.
"You're getting a high yield and also more lambs, that's the big trade off ," he says. "You can have an impact on fleece weight because you can have an increased number of lambs, and lambs that don't lie down and die."
At the CSIRO research station in Armidale, investigations are continuing into the viability of a vaccine that may be able to prevent flystrike, as well as the possibility of breeding more plain-bodied sheep with bare breeches to remove the risk of flystrike altogether. But Dr Sabine Schmoelzl, the group leader for sustainability and welfare with CSIRO agriculture and food, says genetics alone may not solve the problem.
"Like many diseases, it's often not possible to eradicate something completely, but you can reduce it so much that you can deal with the cases you have," she says.
New Zealand banned mulesing in 2018, but Schmoelzl says the different climate and geography of Australia makes it hard to simply copy the approach across the Tasman.
"We don't want to just expose sheep to flystrike in order to make us feel better because we are not mulesing, but on the other hand the sheep are actually now sick," she says.
"It is likely that it will be difficult for wool to get sold if mulesing at least doesn't change, let's put it that way."
Lionel Plunkett, the business intelligence and insights manager at the Australian Wool Exchange, which reports wool sales at auction, says the exchange has seen a 5% increase year-on-year for non-mulesed wool bales coming to sale.
"It's a combination of push and pull," he says. "People are coming onboard with non-mulesed wool, there is the demand in terms of an increased price having an effect.
"A lot of growers can see the writing on the wall, they're getting ahead because they can see the sustainability aspects as becoming very important."
"We do have people who want this to move at a quicker pace, but the breeding can take generations," he said.