It’s like a scene from a gruesome science-fiction film: strange, ugly creatures bursting out from the back of their disfigured mother and then starting to eat one another. But it’s not science fiction, it’s science fact – it’s just how the Surinam toad chooses to gives birth.
The Surinam toad looks, upon first glance, like a horrible evolutionary accident. Its highly flattened body makes it seem as though it has been squashed by a car. It has a triangular shaped head with tiny, oddly-positioned eyes. It has small, thin front legs and short, stout back legs. Its front toes have tiny, star-like appendages, which help it to detect movement in the water and grab passing prey.
Like the majority of amphibians, the Surinam toad has its eggs fertilised externally, rather than inside the female’s body. So how do we get from eggs that are deposited from the female into the water to baby toadlets emerging from her back? The four stage procedure is as follows:
1. First of all, the male Surinam toad needs to find a mate. Unlike most frogs and toads, he doesn’t have a vocal sac and so he cannot call to attract a female. Instead, he produces sharp clicking noises by snapping the hyoid bones in his throat. In the dense medium of water, these sounds travel far and it is usually enough to pique the interest of nearby females.
2. Female and male toad start doing loop-the-loops in the water, with the male hugging the female from behind (this is known as amplexus). The female releases her eggs from her body, which land on the male’s belly and then pass onto the female’s back as the loop continues. It is there that the male releases his sperm to fertilise the eggs.
3. The male hugs the female still tighter and presses the mass of eggs onto the female’s thick, spongy skin. The pair may stay like this for hours, and the long bout of hugging allows the eggs to slowly embed themselves into the skin on the female’s back. After thirty hours or so, the skin on the back has extended over the top of the eggs and is once again smooth and un-pitted.
4. Eventually, each egg is sealed inside its own little chamber in the flesh of the female’s back. Nourished by yolk contained within the eggs, the young develop rapidly. After fifteen or so weeks, they break out of their brood chambers and emerge from their mother’s back. By the time they are born, the tadpoles have already become miniature toads and can look after themselves. They are so independent that they can, if need be, immediately start feasting on their own brothers and sisters.
Here’s a great video that shows the emerging toadlets in action.
This may seem like an unorthodox way of looking after your 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. Of course, it’s probably not doing their mother’s back much good…