Echidnas eat ants. It's fundamental to their lifestyle, so an echidna with an allergy to ants is as doomed as a dolphin that can't consume fish or a horse that reacts to grass. Fortunately for the Tachyglossus aculeatus named Matilda, she lives in Healesville Sanctuary in Victoria, Australia, with lots of caring attendants who were willing to go the extra mile to save her, including developing a vaccine.

Matilda's burrow was accidentally dug up when she was just a puggle (baby echidna) too young to survive alone. At the sanctuary she quickly won hearts thanks to her very unechidna-like extroverted personality. However, the keepers became concerned about her puffy red eyes and loss of hair and skin on her underside. After eliminating common sources of echidna disease, such as ticks and fungal infections, the sanctuary team consulted veterinary dermatologists at Melbourne Veterinary Specialist Centre (MVSC), who suggested allergen screening.

This revealed a surprising variety of allergies, including to paperbark trees common in echnida habitats. Most astonishing, however, was that Matilda was allergic to a distinctive ant molecule called formic acid.

Sanctuary vet Claire Madden told IFLScience that “this is the first known case of a definitive ant allergy in an echidna.” Many captive echidnas are already fed on a powdered diet made into paste, but Matilda was encountering ants in the enclosure she shares with another echidna and a koala, using her powerful claws to rip ant nests open before hoovering up the ants with her formidable tongue.

“We'd never deprive an animal of its natural behavior,” Madden said, even if it was possible to keep Matilda's habitat ant-free.

Instead, the MVSC created two vaccines, which gradually boosted Matilda's exposure to her most troubling antigens until her immune system adapted and her symptoms passed. Six months after her last injection, her handlers are ready to declare success. Although she appears to be cured, the sanctuary says there is no prospect of releasing Matilda, as she is far too fond of human company to be safe in the wild. Madden told The Guardian that “she has lost the ability to identify that she is in fact an echidna.”

It is not known whether Matilda's allergy is genetic, or a product of being separated from her mother so young. Echidnas used to lay eggs in captivity only rarely, but recent successes elsewhere have encouraged staff to hope they may one day have Matilda puggles, and they'll be ready if they see similar symptoms.

Madden told IFLScience the MVSC did much of the work pro bono, but the time that went into Matilda's care, diagnosis, and treatment would have cost many thousands of dollars if fully charged. None of it is regretted, however. “All our animals are priceless,” she said.