Amphibians
Common Midwife Toad
Alytes obstetricans · also called common midwife toad, bell toad
The common midwife toad is a small, unassuming European amphibian with one remarkable habit: the father carries the eggs. He winds the fertilised string of eggs around his own back legs and totes them about on land for weeks, tending them, before slipping into a pond to release the tadpoles.
Overview
Common midwife toads live across western Europe, from Iberia to Germany and Switzerland, in almost any habitat with loose or stony ground for burrowing near water — woodland, meadows, gardens, quarries, dry-stone walls, and mountain slopes to over 2,000 metres. They are nocturnal and mostly terrestrial, hunting small invertebrates and sheltering by day in burrows and crevices. The male’s soft, bell-like “poo…poo…poo” is a characteristic sound of a European spring night.
The carrying father
Mating happens on land. The female produces a string of 20–80 large eggs, the male fertilises them, and then he wraps the string around his ankles and thighs. He carries it for three to six weeks, going about his life — feeding, moving, calling — with the eggs attached. A male may carry two or three females’ clutches at once.
Keeping the eggs alive out of water
The male manages moisture, visiting damp refuges and shallow water every day or two to rehydrate the eggs through his skin. The egg jelly and his skin secretions have antifungal properties, so the clutch loses far fewer embryos to mould than an exposed clutch would. When the tadpoles are ready, he releases them into a pond or slow stream.
A place in scientific history
The midwife toad was central to the Paul Kammerer affair of the 1920s, in which claimed evidence for the inheritance of acquired traits was exposed as faked with injected ink — a lasting cautionary tale, retold in Arthur Koestler’s book.
Status
The common midwife toad is Least Concern but declining in places, and has been hit hard by the chytrid fungus in parts of Spain.
Common Midwife Toad: common questions
Why is it called the "midwife" toad?
Because the male takes on the role of carer for the eggs, which in the 18th and 19th centuries struck naturalists as him assisting the female like a midwife. During mating, which happens on land, the female extrudes a string of large eggs, the male fertilises them, and then he deliberately works the egg string up and around his hind legs until it is wound securely about his ankles and thighs. He carries it there — feeding, moving about, and calling — for the next several weeks. It is one of the clearest cases of paternal care in any amphibian, and unusual in that the eggs are kept out of water for almost their whole development.
How does the male keep the eggs alive on land?
He manages their moisture and their microbes. Every day or two he seeks out a humid refuge or a shallow puddle and absorbs water through his skin, which rehydrates the eggs wrapped around his legs; if the eggs dried out they would die. The eggs themselves have a jelly coat, and the male's skin produces secretions, that both have antimicrobial and antifungal effects, so the developing embryos are far less likely to be lost to mould than a clutch left in the open would be. When the tadpoles inside the eggs are fully formed and start to wriggle, the male goes to a pond or slow stream and releases them into the water, where they finish growing.
Is the midwife toad a true toad?
Not in the family sense. It belongs to Alytidae (the "painted frogs" and midwife toads), a small, ancient European and North African family separate from the true toads (Bufonidae). It looks toad-like — squat, warty, terrestrial — but it has vertical pupils, lacks the large parotoid glands of true toads, and of course has the egg-carrying behaviour, which no true toad shows. There are several midwife toad species; the common midwife toad is the most widespread.
Why does the midwife toad matter in the history of science?
It was at the centre of a famous scientific scandal. In the early 20th century the Austrian biologist Paul Kammerer claimed that midwife toads bred in water for several generations developed dark "nuptial pads" on their forefeet, and that this acquired trait was inherited — apparent support for Lamarckian evolution against Darwin and Mendel. In 1926 a examination of his last specimen found the black markings had been faked with injected India ink. Kammerer denied wrongdoing but killed himself weeks later. Whether he committed the fraud or was framed is still debated, and the affair became a cautionary tale about wishful science, retold in Arthur Koestler's book "The Case of the Midwife Toad."