Freaky Frogs

Surinam Toad

A Surinam toad in a tank
Image Source: Stan Shebs

Perhaps I’m being a little unfair calling this series of articles ‘Freaky Frogs’. After all, the species that we’ve already looked at have certainly been bizarre or remarkable in one way or another, but are they freaky? That’s debatable. However, the focus of today’s post – the Surinam toad – is undeniably, unequivocally, unquestionably freaky. Case in point: the young of this species burst out from the back of their disfigured mother and then start eating one another. It may seem like a scene lifted straight from a gruesome science-fiction film, but this is science fact; it’s simply how the Surinam toad gives birth. It’s top-notch freakiness, no doubt about it – and I love it so much.

(Warning: Sufferers of trypophobia may wish to steer clear of this creature.)

At first glance, the Surinam toad seems like a horrible, grotesque evolutionary accident. (And yes, before there’s any confusion, that flat, grey shape in the picture above is the animal in question.) Its extremely flattened body makes it look as though it has been squashed in a road accident. Its tiny, lidless eyes almost seem like they have been put in the wrong position on its wide triangular-shaped head. Small, thin front limbs, which are held out in front of it rather than under its body like in other frogs and toads, are used to sweep morsels of food into its large mouth. It certainly won’t be winning a beauty contest anytime soon, that’s for sure – but that doesn’t matter because the Surinam toad is quite content lying motionlessly at the bottom of South American ponds and swamps, often on top of one another, looking a bit like rotting leaves.

Like the majority of amphibians, the Surinam toad’s eggs are fertilised externally rather than inside the female’s body. So how do we get from point a) eggs being deposited by the female into the water, to point b) baby toadlets emerging from her back?

First of all, as is often the case, the male needs to attract a female. He does not call to attract a mate because he doesn’t even have a vocal sac. Instead, he produces sharp clicking noises by snapping the hyoid bones in his throat, which the females seem to find quite alluring.

Once a pair come together, the male holds on to the female from behind, an embrace called amplexus that is seen in many frog species. Then the female kicks with her legs so that the pair, still together, soar upwards through the water in a slow, elegant somersault. Midway through the arc, when the pair is upside down in the water and the male is below the female, she extrudes a few eggs, which fall onto the male’s belly. Completing their sexual somersault, the toads flip to their original position. The male relaxes his grip slightly and allows the eggs to roll onto the female’s back, where they stick. He releases his sperm to fertilise the eggs and presses them into her thick, spongy skin, sometimes spreading them out over her back using his splayed hind feet.

Again and again, this arching leap is performed until, when the acrobatic ballet is complete, a hundred or so eggs are fixed in an even carpet on the female’s back. The skin beneath them begins to swell and soon the eggs are embedded in it. A membrane rapidly grows over them. Within 30 hours, the eggs have disappeared from sight and the skin on the female’s back is smooth and un-pitted once more.

By now, each egg is sealed inside its own little chamber within the flesh on the female’s back. When the eggs hatch, the tadpoles remain inside their individual cells, nourished by yolk. Eventually, the tadpoles transform into tiny toadlets, which may become so active within their honeycomb-like pockets that the skin on the female’s back ripples continuously.

Finally, the toadlets emerge from their brood chambers. For the mother, this is literally back-breaking labour – it may take the youngsters up to a day to fully break through her membranous skin. For a while, they remain half-in, half-out, their tiny arms waving in the water. But when they do manage to wriggle free, their mother’s maternal care abruptly comes to an end; the toadlets immediately begin solitary lives, sometimes even feasting upon their own newly-emerged brothers and sisters.

A preserved museum specimen of a female Surinam toad with toadlets emerging from her back
This preserved specimen at the Natural History Museum of Vienna shows a female Surinam toad with toadlets emerging from her back. Although the young generally emerge from their pouches under their own power, the female may occasionally exert pressure to force them out.
Image Source: Dein Freund der Baum

Brooding your offspring within the skin on your own back may be an unorthodox way of looking after young, but the female Surinam toad’s hospitality is worth it – many more toadlets will survive than if her eggs were simply abandoned in the water.

For me, the Surinam toad is pretty much peak freakiness. It’s weird, extraordinary and horrifying in equal measure. But we’re not done with freaky frogs yet. Next time, in a special post, we’ll be taking one last look at frogs with bizarre breeding behaviour – and then after that, we’ll be moving on to investigate anurans living in extreme environments!

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