The echidna has spines like a porcupine, a beak like a bird, a pouch like a kangaroo, and lays eggs like a reptile. Also known as spiny anteaters, they're small, solitary mammals native to Australia, Tasmania, and New Guinea. They're usually between 12 and 17 inches long and weigh between 4 and 10 pounds.

There are two genera of echidna. The short-beaked echidna (Tachyglossus aculeatus) belongs to the genus Tachyglossus, while the three species of long-beaked echidna belong to the genus Zaglossus. Short-beaked echidnas are smaller and have longer hair than long-beaked echidnas. Long-beaked echidnas, native to New Guinea, include one species named after Sir David Attenborough (Z. attenborough).

These animal oddities are elusive, but the more scientists discover about echidnas, the weirder it gets. Read on to see for yourself.

1. Their spines are actually modified hairs. Echidnas' bodies (with the exception of their undersides, faces, and legs) are covered with 2-inch long spines. Fur between the spines provides insulation.

2. Echidnas live slow and long. Echidnas have the lowest body temperature of any mammal, 32__°__C (89__°__F). Their body temperatures are not controlled in the same way as that of other mammals, and can fluctuate by up 6–8°C over the course of the day. Their long life spans — up to 50 years in captivity, with anecdotal reports of wild animals reaching 45 years — are due to their low body temperature and slow metabolism.

Tachyglossus aculeatus setosus. Photo: JKMelville, via Wikimedia Commons

3. Male echidnas have a bizarre, four-headed penis. You might wonder how you mate with a four-headed penis. During sex, two of the heads shut down while the other two grow bigger to fit into the female's two-branched reproductive tract. Males alternate the heads they use between matings. This one-sided ejaculation may play a role in sperm competition, as many males attempt to fertilize the same female. In another possible adaptation for sperm competition, echidna sperm form bundles that swim faster than individual sperm cells.

If you're curious about what the echidna's penis looks like (and really, who isn't?), you can find photos here and watch a video here.

4. Echidnas form mating trains. A strange process marks the start of echidna breeding season. Males line up nose to tail behind a single female, forming a train of up to a dozen individuals. Trains can last more than a month, with males dropping out and rejoining. When the female is finally ready to mate, the males dig a trench in the ground around her. The males compete for mating honors by pushing each other out of the trench. The last one remaining gets to mate with the female.

Male echidnas may also mate with hibernating females. Males sometimes wake up from hibernation early and sneak into the burrows of still-hibernating females. This can result in female echidnas waking up from hibernation and finding themselves pregnant.

Tachyglossus aculeatus. Photo: JJ Harrison, via Wikimedia Commons

5. Echidnas are egg-laying mammals. Along with the platypus, the echidna is a member of the monotremes, an order of egg-laying mammals found in Australia. After mating, a female echidna lays a single, soft-shelled, leathery egg, about the size of a dime, into her pouch. Ten days later, the baby echidna (called a puggle and smaller than a jelly bean) hatches.

6. Echidnas are mammals without nipples. Like all mammals, echidnas feed their young milk. But they do it without nipples. Instead, female echidnas have special glands in their pouches called milk patches that secrete milk, which the puggle laps up.

7. They are electroreceptive. Like the platypus, the echidna has an electroreceptive system. While the platypus has 40,000 electroreceptors on its bill, echidnas have only 400-2,000 electroreceptors on their snouts.

8. They're toothless but make up for it with their tongues. At the end of their slender snouts, echidnas have tiny mouths and toothless jaws. They use their long, sticky tongues to feed on ants, termites, worms, and insect larvae. (The short-beaked echidna earned its scientific name, *Tachyglossus, *meaning "fast tongue," from its way of rapidly darting its 6-inch tongue in and out of its mouth to slurp up insects). Since they have no teeth, echidnas break their food down with hard pads located on the roof of the mouth and back of the tongue. (Watch a video of an echidna hunting here.)

Tachyglossus aculeatus. Photo: I, KeresH, via Wikimedia Commons

__9. ____ Echidnas have unusual brains. __ The echidna has a very large brain for its body size. Part of this might be due to their enlarged neocortex, which makes up half of the echidna's brain (compare this to about 30 percent in most other mammals and 80 percent in humans).* ***

It was long thought that echidnas didn't enter rapid eye movement (REM) sleep at all, the type of sleep associated with dreaming in humans. But recently researchers found echidnas will experience REM sleep if they're at the right temperature. They enter REM sleep at around 25 °C (77 °F), but not at higher or lower temperatures.

10. They host the world's largest flea. *Bradiopsylla echidnae, the echidna flea, is thought to be the world's largest flea at 4 mm (0.15 inches) long. ***





References and Other Resources:____

Bradiopsylla echidnae*. *Encyclopedia of Life. Retrieved June 2014.

Cason, M. (2009). "Tachyglossus aculeatus". Animal Diversity Web. Retrieved June 2014.

Dell'Amore, C. (2014). Spiky Baby-Killers: Echidna Secrets Revealed. National Geographic Weird & Wild blog. Retrieved June 2014.

Johnston, S. D., Smith, B., Pyne, M., Stenzel, D., and Holt, W. V. (2007). One-sided ejaculation of echidna sperm bundles. American Naturalist 170(6): E162-E164. doi: 10.1086/522847.

Nicol, S. C., Andersen, N. A., Phillips, N. H., and Berger, B. J. (2000). The echidna manifests typical characteristics of rapid eye movement sleep. Neurosci. Lett. 283(1): 49–52. doi:10.1016/S0304-3940(00)00922-8.

Rismiller, P. D. and McKelvey, M. (2000). Frequency of breeding and recruitment in the short-beaked echidna, Tachyglossus aculeatus. Journal of Mammalogy 81(1): 1-17.

Sorin, A. and P. Myers (2001). "Tachyglossidae." Animal Diversity Web. Retrieved June 2014.

Stewart, D. (2003). "The Enigma of the Echidna." National Wildlife. Retrieved June 2014.

"Tachyglossidae (Short-beaked echidnas)." Encyclopedia of Life. Retrieved June 2014.

"Zaglossus (Long-beaked echidnas)." Encyclopedia of Life. Retrieved June 2014.