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Spiky Baby Killers: Echidna Secrets Revealed

An egg-laying, spiny mammal with a four-headed penis is already pretty bizarre, but it turns out short-beaked echidnas are even stranger than we thought. Weighing up to nine pounds (four kilograms) and resembling a big hedgehog, the short-beaked echidna is one of only three species of monotremes—or egg-laying mammals—left in the world, along with the platypus...

An egg-laying, spiny mammal with a four-headed penis is already pretty bizarre, but it turns out short-beaked echidnas are even stranger than we thought.

Weighing up to nine pounds (four kilograms) and resembling a big hedgehog, the short-beaked echidna is one of only three species of monotremes—or egg-laying mammals—left in the world, along with the platypus and long-beaked echidna. Unlike hedgehogs, echidnas brandish “spines” that are actually modified hairs.

One of Australia‘s most widespread mammals, the short-beaked echidna is versatile, thriving everywhere from the tropics to the island of Tasmania (map), where University of Tasmania zoologist Stewart Nicol has been tracking the animals’ behavior with radio transmitters since 1996. (Also see “Primitive and Peculiar Mammal May Be Hiding Out in Australia.”)

Before Nicol came along, “surprisingly little work” had been done on echidnas. But the more that he probed into echidnas, the “more fascinated I became,” he said.

We caught up with Nicol, a National Geographic grantee, to learn about the latest unusual echidna discoveries—and why he’s found them to be “spiky baby killers rather than friendly, furry creatures.”

1. Echidnas live as long as 50 years.

Their longevity is due to “living life in the slow lane,” Nicol said, which means their metabolism is very slow and their body temperature very low—about 89°F (32°C). Nicol has been tracking some individual echidnas for 18 years.

A photo of an echidna.
An echidna on Australia’s Kangaroo Island. Photograph by Thorsten Mise.

“They seem to have personalities—some of them get quite grumpy and annoyed when you handle them, others are very docile. Some of them will pee all over you when you pick them up.”

Thanks to their unusually large and complex brain, the mammals are also smart: Nicol recounted one incident in which his team found a wild echidna that had lost its radio transmitter and needed a new one. (Watch a video of an echidna on the hunt.)

When the critter spotted the team from across a field, “you could see it run like crazy because it knew what was happening. It was going, ‘Oh, shit, here we go again.'”

2. Male echidnas may mate with hibernating females. 

The solitary animals often have overlapping ranges, as Nicol’s GPS data has shown. “The males have great big home ranges and spread themselves out to make sure they have access to as many females as possible,” he said. (See “Pictures: 14 Rarest and Weirdest Mammal Species Named.”)

Both males and females hibernate in burrows, but the males often wake up earlier and sneak into females’ burrows, where they mate with the still-hibernating animals. Females can even wake up pregnant, perhaps with no memory of mating (a phenomenon Nicol has dubbed “cool sex”).

In general, females are promiscuous, mating with a lot of males, and continue to mate even when pregnant.

“It is not clear how much choice the females have in this,” Nicol noted.

3. Males have “enormous testes.” 

During mating season, testicles can make up as much as one percent of their body mass. (Since the organs are inside their bodies, not dragging along the ground, Nicol and his team had to catch the animals and use ultrasound to measure the size.)

Big testes usually imply stiff competition for promiscuous females, which is certainly true for echidnas—it’s common to see up to ten males pursuing an individual female. Nicol added that he’s lifted a log in Tasmania and found three or four male echidnas hanging out with a single female. (Related: “Bigger Testes Can Offer a Competitive Edge.”)

Another example of the intense competition for females is what happens to the testes during hibernation. In other hibernators the testes shrink during hibernation and have to be regrown when the animal warms up. Echidnas regrow their testes before they enter hibernation, ensuring they are ready for action when they rewarm.

4. Males may kill babies.

After a three-week pregnancy the female echidna makes a nursery burrow, where she lays her egg directly into her pouch, incubating it for ten days until it hatches into a baby.

The female then feeds the baby with milk for another five to six weeks, before she leaves the burrow to forage. She returns at five- or six-day intervals to feed the baby, and only stays with it for a few hours.

While the mother is in the nursery with her egg or the newborn baby males may try to break into the burrow, presumably to mate with the female again.

If this happens the young dies—“we don’t know exactly how, but presumably just by being dislodged from the mother’s pouch”— which would make the female come into heat again.

“The death of the young is an essential part of his strategy because it will remove a young that is not related to him from the population, while giving him a chance to impregnate the female himself.”

Interestingly, the only males that break into the nursery burrows are the ones she hasn’t mated with yet, suggesting the males know which females they’ve already mated with.

5. Echidnas don’t have nipples… but do have supermilk.

In most mammals, a nipple is a tidy way for a baby to ingest milk without spilling it. In nipple-less echidnas, babies suck from a “milk patch,” an area that oozes milk.

“You can hear the slurping sounds from outside the burrows,” Nicol said.

Since the milk spills out around the warm pouch, potentially harmful bacteria can form. Echidnas have evolved a defense for this, which Nicol has discovered: Their milk contains proteins that inhibit the growth of harmful bacteria, thus protecting their young from illness.

Overall, Nicol said, his research on Tasmanian echidnas boosts overall knowledge of the animals, which could help save the critically endangered long-beaked echidna of New Guinea.

What do you think is the weirdest thing about the echidna?

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Meet the Author

Christine Dell'Amore
Christine Dell'Amore, environment writer/editor for National Geographic News, has reported from six continents, including Antarctica. She has also written for Smithsonian magazine and the Washington Post. Christine holds a masters degree in journalism with a specialty in environmental reporting from the University of Colorado at Boulder. Her book, South Pole, was published in 2012.