“…[T]he goddess fierce Echidna who is half a nymph with glancing eyes and fair cheeks, and half again a huge snake, great and awful, with speckled skin, eating raw flesh beneath the secret parts of the holy earth. And there she has a cave deep down under a hollow rock far from the deathless gods and mortal men.”
– Hesiod, Theogeny, 301-304.
In his epic poem Theogeny, the Ancient Greek poet Hesiod (~750-650 BCE) recounts the origins and genealogies of the Greek gods. Among the gods he writes about is the goddess Echidna. Echidna, according to Hesiod, was a drakaina – a female dragon whose appearance is halfway between a human woman and a snake. According to myth, Echidna and her mate Typhon attacked Zeus and the other Olympians. This was always a bad idea, and when they lost, Zeus imprisoned Typhon beneath Mount Etna for eternity. But he left Echidna free, with the caveat that any children she bore would be monsters, to be used by the gods to test heroes.
And Echidna was prolific. Among her children she counted Cerberus, the dog which guarded Hades; the Chimera, a lion-goat-snake monster; Scylla, the sea-monster which threatens Odysseus in the Odyssey; the Nemean lion, killed by Heracles; and the Sphinx. Imagine the family reunions. Eventually, a giant killed Echidna while she slept. But luckily for us, her spirit lives on, in the form of a slightly cuter monster: the echidna.
Echidna’s (also called spiny ant eaters) are a complex of four species, forming the family Tachyglossidae. They are monotremes, the most ancient group of mammals, which means they already have a few strange characteristics. The word monotreme means ‘one opening’; like reptiles, monotremes have a cloaca – a single duct from which they urinate, defecate, and reproduce.
Echidnas, like other monotremes, don’t reproduce like a regular mammal. No live birth here – monotremes lay eggs. This is a cue to just how old they are. The genes that govern egg-laying behaviour in monotremes are similar to those that govern egg laying in birds – and mammals diverged from ancestral birds over 200 million years ago. Monotremes are a throwback to a different age, so we can forgive them for being a bit weird. And anyways, once hipsters discover how retro they are, they’ll become cool again.
Echidnas live in New Guinea and Australia, and eat termites and ants. They use powerful claws to dig into nests and anthills, and then root around with their long nose. Like the South American anteater, they use their long, sticky tongue to drag ants and termites out of their holes. Echidna’s are similar morphologically and behaviourally to South American ant-eaters, but they are only distantly related. It’s another example of convergent evolution, like the aye-aye and the bilby, where identical environmental pressures in two different places has produced similar animals to exploit the habitat.
Like other monotremes, echidna’s are shy and retiring creatures. In the summer they forage nocturnally, but in winter they tend to forage during the day – possibly to try and keep their body temperature up. For a long time, biologists thought that echidna’s had problems with thermoregulation – the mammal’s ability to maintain a constant internal body temperature (the trait that makes us ‘warm-blooded’). The core body temperature of most placental mammals is 37°C (98.6°F). Even slight deviations away from this mark have serious ramifications – hypothermia if the body temperature falls, and hyperthermia (fever, heatstroke) if the body temperature rises. Both of these conditions very rapidly become fatal. When researchers measured the body temperature of echidna’s, they thought something must be very wrong. Echidna’s maintain their core body temperature at a brisk 30.7°C (87.8°F). In other mammals, this is moderate to severe hypothermia: extremities turn blue, and mental confusion begins to appear. Any further reduction in temperature is likely to cause major respiratory failure.
Echidna’s do just fine with this temperature. The discovery forced researchers to reassess what biology they considered ‘normal’. And since, really, echidna’s are more ancestral than placental mammals, maybe they’re ‘normal’, and we hot-blooded placental mammals are the strange ones.
But then again, maybe not.
Echidna reproduction is a strange and harrowing thing. The females are fairly normal (aside from that whole ‘one opening egg-laying’ thing), but in the males you can find a good reason why they might be named after the mother of all monsters.
The male echidna has a four-headed penis. It’s just as horrifying as it sounds. But not to worry, only two of those heads are active at any one time. And of the two active heads, only one will ejaculate. The active and ejaculating heads change every time the echidna copulates: it’s like Russian Roulette, but somehow even more disturbing.
But they’re not finished after ejaculating. Echidna sperm has some strange characteristics too. Female echidna’s are only reproductively active for about one week per year, so during that brief spell, many males will line-up to have a go. This means a lot of sperm in the female echidna’s reproductive tract, but only a single, individual sperm, from one male, will fertilize the egg.
So the male echidna sperm must race to the egg. And the best way to do this is to team-up. Sperm from individual males clusters together into a sort of ‘Flying V’ of sperm, able to sweep through the reproductive tract more rapidly than a sperm travelling by it’s lonesome. Teamwork pays off.
Once the female has been fertilized, she gestates an egg for 20 days, and then incubates it either in a pouch, or in a burrow, for another 11 days. The choice of pouch or burrow depends on the stability of the external temperature. If the temperature outside is fluctuating dramatically, she’ll use the pouch. If the temperature is more stable, she’ll keep the egg in a burrow. When the babies are born, she nurses them by exuding milk through her skin, like sweat (monotremes don’t have nipples).
Echidna’s are one of the most ancient form of mammal, and understanding them allows scientists to grab a brief glimpse into the haze of our long distant past. But beyond that noble goal, they’re weird looking and act funny, and that’s more than enough reason to consider them here.
I’m going to switch to updating twice a week, Thursdays and Sundays, rather than three times a week. Writing a thesis and this blog at the same time is proving tricky.