The Kangaroo Island echidna (Tachyglossus aculeatus multiaculeatus) is surely among the world’s most bizarre creatures. A subspecies of the short-beaked echidna of mainland Australia, this diminutive mammal makes its home on an island off Australia’s southern coast. It’s covered in sharp, hollow hairs that look like porcupine quills, has an anteater-like tongue and no teeth, and is among the few mammal species that lay eggs. Strangest of all, though, may be echidnas’ mating rituals and anatomy.

When breeding season rolls around during the southern winter, female echidnas release pheromones that attract usually-solitary males from miles around. The males form a line—called a “love train”—and dutifully follow the female on days-long hikes over Kangaroo Island’s white-sand beaches and through its eucalyptus forests. When the female decides she’s ready, she lies down and relaxes while the males dig a circular trench around her, then attempt to shove each other out of the ring like tiny sumo wrestlers.

Finally, the victorious male brings out his secret weapon: a penis with four heads on a single shaft. When the echidnas mate, two of the heads go limp while the remaining two enlarge to fit inside the female’s branched reproductive tract. If the male later mates again, he’ll alternate and use the other heads. Scientists theorize this could improve his chances of producing offspring, since each head could draw from a different sperm pool. Or it could allow male echidnas to swiftly move from one female to the next, since half of the penis is always ready to go. In one experiment, an anesthetized echidna was able to ejaculate 10 times in a row by alternating heads.

Whatever the reason, these reproductive strategies may contribute to echidnas’ remarkable resilience; as one of the world’s oldest mammals, echidnas have persisted through cataclysmic changes in climate and ecology. And though they now face habitat loss and non-native predators like foxes and feral cats, they seem to be weathering the impacts of anthropogenic climate change fairly well. Take, for example, the bush fires that blackened nearly half of Kangaroo Island’s 440,500 hectares (1.1 million acres) in 2020.

Although the fires killed thousands of koalas (Phascolarctos cinereus) and other wildlife, there were few echidnas among the casualties. When a fire approaches, the animals can quickly dig holes deep enough to insulate themselves from the worst of the heat, then pack the spaces between their spines with dirt to protect their skin from burning. And because echidnas can lower their respiration, metabolism, and body temperature, they can spend long periods of time holed up underground with limited oxygen.

Kangaroo Island echidna expert Dr. Peggy Rismiller says that although the 2020 fires were hot enough to melt the tips of some echidnas’ spines, even very young echidnas whose nursery burrows were directly in the burn zone survived. She documented one female near a nursery burrow soon after the fires abated, likely snatching up insects to eat and then returning to the burrow to nurse the baby echidna, called a puggle, nestled within. A month later, Rismiller saw a juvenile Kangaroo Island echidna emerge from the burrow, unscathed and seemingly undaunted by the charred landscape.