A Judas animals are invasive species that, like the infamous apostle, betray their own kind. Their reward, however, is not 30 pieces of silver but the safeguarding of native biodiversity. The procedure is simple: the Judas animal is caught, radio-tagged and released.

Oblivious to the fact that it is now being followed, it heads off to find a mate, which is then removed. “Along with habitat loss, invasive species are a major cause of extinction,” says P-A Åhlén from the Swedish Association for Hunting and Wildlife Management. “Judas animals are playing an increasingly important role in their eradication.”

The technique is being used with particular success in Sweden to tackle raccoon dogs. These East Asian canids became established here (and in Finland and Germany) after being introduced to the former Soviet Union for their fur, and have been chomping their way through the country’s amphibians and ground-nesting birds at such an alarming rate that the government has employed six professional hunters to cull them. But, given that the species is distributed over an area the size of the UK, the task is easier said than done.

Enter the Judas dogs. “There is no creature more suited to finding a raccoon dog than another raccoon dog,” says P-A. “They are significantly reducing the population.”

Other Judas animals include goats on the Galápagos Islands and Burmese pythons in the Florida Everglades.

Main image: Raccoon dog  © Ryzhkov Sergey, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons