The following is based on: Tomma G. 2024. Giant Australian lizards may help protect sheep from deadly fly-borne diseases. Science July 11.

Some blowflies have an unnerving reproduction method, akin to extraterrestrial parasites from a sci-fi horror film: they deposit their eggs on the bodies of animals, sometimes in open wounds, sometimes on their fur or wool. Infections may result from the young maggots feeding on the host’s skin after the eggs hatch. Sheep are particularly vulnerable to “flystrike,” a potentially lethal illness. The issue causes the Australian sheep market hundreds of millions of dollars’ worth of damage annually.

A study suggests that another Australian animal could potentially provide relief: Researchers report in Ecology and Evolution that large lizards known as heath goannas might lower blowfly populations—and possibly help avoid flystrike on surrounding farms—by scavenging carcasses in the wild that can house the maggots of blowflies. Crucially, the scientists observe that they perform better in this capacity than non-native species, such as cats and foxes.

“The functional roles that large reptiles play in ecosystems is still fairly poorly documented … so this study represents a great contribution,” says Georgia Ward-Fear, a conservation ecologist at Macquarie University who wasn’t involved with the work. “It shows that large reptiles are really important to ecosystem processes.”

The study’s lead author, Tom Jameson, a conservation biologist at the University of Cambridge, and associates started observing behavior around rat carcasses in South Australia to investigate the advantages of the health goannas (Varanus rosenberg) scavenging. “Basically, what this involved was driving around in Australia’s remote areas in pickup trucks carrying a large freezer box filled with dead rats,” Jameson explains.

To provide carcasses for use by various animal species, they erected four distinct feeding stations at each location. They scattered hundreds of these dead rats across the parched terrain, shrouded in low vegetation. In one form of station, the dead animal was left lying around for any scavenger to find. At another station, they fastened the carcass to a cable inside a wire-mesh tunnel, making it accessible only to lizards and snakes. Another station positioned the carcass on a two-meter-tall platform, making it accessible only to birds. Lastly, a different station confined small invertebrates, such as insects, to a cage made of wire mesh on the ground and contained carcasses.

Then, for five days, the researchers set up camera traps in front of each of the 180 feeding stations to observe which scavengers were more active, which arrived first, and which were more effective at removing carcasses. “We’d put these rats out in the Sun, often in 35° heat,” Jameson says. “And you can imagine coming back to that smell after 5 days was not good at all.”

After watching the video, the researchers observed various scavengers, including foxes, cats, goannas, and birds, visiting the carcasses. With 93 scavenging visits, native ravens were the most frequent visitors to the dead rats. Goannas engaged in the most flesh feasts among non-avian species—seven total. Goannas defeated invasive species such as cats and foxes, which have displaced local lizards in many areas, in this scavenging context. They also found these remains a little faster on average than scavengers that are mammals. (Although, once more, birds were usually the first to arrive.)

The number of blowfly maggots that lived in a rat’s carcass fell off every time it was scavenged, indicating that scavenging may disrupt the life cycle of these bothersome insects. “We find that any carcass fed on by heath goannas has close to zero maggots in it,” Jameson notes.

Scavenging activity was generally higher in locations where nonnative scavengers are nearly nonexistent, according to the researchers’ findings. In terms of how native species assist the ecosystem, Jameson says it was “a nice surprise to show… the value of native species over these invasive species.”

Native scavengers would have more room if non-native animals, such as foxes and cats, were eliminated from the habitat, according to Eric Nordberg, a University of New England researcher who was not involved in the study. “A great goal to have is to rid the country of the invasive, introduced predators so that we can get back to our native species that can fill that same role.”

According to the researchers’ findings, reintroducing healthy goannas to areas where they have become extinct may help reduce blowfly numbers in the region. “Hopefully this is going to start a bit of a conversation about the role of reptiles as scavengers” in keeping ecosystems healthy, Jameson says.

It is unclear, though, if the intervention will lessen the prevalence of blowfly parasitism in sheep, according to Ward-Fear.

She adds that the next step would be for scientists to examine the scavenging behavior around “real carrion,” like kangaroos, and see if the huge reptiles inhabit the exact locations as those naturally occurring carcasses.