A clever technique is being used to track down an elusive and “specialist” invasive predator wreaking havoc on a remote island off the coast of Australia.
The hard-to-spot wolf snake, also known as Lycodon capucinus, is responsible for the decimation of native wildlife populations since it arrived on Christmas Island, an Australian territory in the Indian Ocean, over 40 years ago.
Authorities are racing to figure out how to track the hard-to-spot invader, which occupies every part of the landscape — it lives both underground, above ground and in the trees, to ultimately get rid of it.
In a new tactic, a “play pen” for the snake was created in the hope of tracking the species using environmental DNA (eDNA). Once scientists can track down the snakes, they have a better chance of reintroducing threatened lizards and skinks native to the island.
“The only way to reintroduce them back into their homes is by controlling the wolf snake,” Brendan Tiernan, the island’s senior threatened species program coordinator, told Yahoo News.
National park worker Jake Haboer processing eDNA samples left by invasive wolf snakes. Source: Christmas Island National Park
Why are wolf snakes so bad for Australia?
The wolf snake, which is commonly found in the Indo-Australian archipelago, was first detected on the island in 1988 near the wharf. “They would have arrived on one of the ships that came in from the north, from either Indonesia or Malaysia,” Tiernan explained.
“Once they arrived, there was either one female who was pregnant or a male and female, and they just populated the island from there,” he said.
Within 30 years, endemic species on the island, like the blue-tailed skink and lister gecko, were lost. Sadly, with the absence of any type of snake-like predator, native animals became “naive and unable to avoid”. It meant that when the “dreaded wolf snake” arrived, they were easily picked off and eaten.
Fortunately, two of the species were secured with captive populations, and the focus now is on finding and, hopefully, one day eradicating the dreaded invader. But there are very few examples of invasive snakes around the world, and of those, “no one” has successfully managed to control or eradicate them.
In the Pacific Ocean’s US territory of Guam, Australia’s brown tree snake was accidentally introduced after World War II and decimated populations of native forest birds and reptiles.
“They have attempted to control and eradicate brown tree snakes and thrown millions of dollars [at the problem] and come up empty,” Tiernan said.
The rare blue-tailed skink once thrived on Christmas Island but sadly wild populations are now extinct. Source: Parks Australia
New strategy to find invasive snakes
But for Tiernan, not all hope is lost.
“It’s about being innovative,” he said. “Wolf snakes are very cryptic, can climb anything and hide anywhere. One of the hardest things is detecting them.”
Because the animals are cold-blooded, thermal cameras can’t be used to track them down. Trapping is also difficult, so it means that “chance encounters” have been the most reliable method.
With the help of the snake “play pen”, the team are attempting to collect eDNA, tiny fragments left behind as animals move through the landscape.
“Environmental DNA is one of those tools we might be able to [use],” he said. In a controlled environment, scientists found that the snakes would leave eDNA on a sandpaper surface.
“Now that we’ve proven we can detect them in a controlled environment, we want to figure out how we can detect wolf snakes in a wild and uncontrolled environment,” Tiernan said.
The theory behind the play pen is that when snakes encounter a fence, “they’ll follow it in the wild”. So sandpaper eDNA stations were left along the fenceline of the pen to collect data about the snakes.
Remarkably, cameras confirmed that snakes did follow the fence line and interact with the eDNA stations, and now scientists are analysing the samples, which will help with the next steps in tracking down the snakes.
While it may not result in the snakes being caught and removed, Tiernan said it might help inform where native species reintroduction does occur.
“It might help us understand where the wolf snakes are now across the landscapes,” he said. “If we can find the areas where they are least abundant, and those areas that are suitable for our lizards we might be able to release our lizards in conjunction with wolf snake control.”
The goal remains to eradicate wolf snakes and re-release the skinks and geckos into the wild.
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