Amphibians
Midwife Toad
Alytidae · also called midwife toads, bell toads
Most frogs abandon their spawn the moment it is laid. The midwife toad does the opposite: the father winds the whole string of eggs around his back legs and carries it for a month or more, sheltering in a burrow by day and dipping the clutch in a pond each night, until the tadpoles are ready to be let go.
Overview
Midwife toads are the family Alytidae, small European and North African frogs of stony hillsides, old walls, quarries, and montane meadows. They are night-hunting insectivores, and the family is an ancient branch of the frog tree — along with the tailed frogs and New Zealand’s Leiopelma, among the most primitive living frogs. The male’s bell-like call gives the alternative name “bell toad”.
The carrying father
After the female lays her string of large eggs and the male fertilises them, he works the string around his ankles and thighs and carries it on land for three to six weeks, keeping it moist and safe, then releases the hatching tadpoles into water. Male-only parental care is rare among frogs, and the midwife toads are its classic example.
A scientific scandal
In the early 1900s, Paul Kammerer claimed midwife toads bred in water developed inherited traits of water-breeding frogs — apparent support for the inheritance of acquired characteristics. In 1926 the key specimen was found to have been faked with injected ink, and Kammerer killed himself weeks later. The “Case of the Midwife Toad” is still argued over.
Status
Midwife toads as a family are Not Evaluated, trend decreasing. The common midwife toad is widespread but declining in the north, and the Iberian and Majorcan species have small ranges — the Majorcan midwife toad, thought extinct until living animals were found in mountain gorges in 1980, is now the focus of a captive-breeding programme against the chytrid fungus.
Midwife Toad: common questions
Why is it called a midwife toad?
Because of the male's role in tending the eggs, which reminded early naturalists of a midwife assisting at a birth. After mating, the male takes the female's string of eggs and winds it around his hind legs, then carries the clutch about with him for several weeks, keeping it damp and safe, and finally helps the young into the world by lowering the eggs into water as they are about to hatch. The name is a little misleading, since a midwife attends someone else's birth while this toad is caring for its own offspring, but the image of a male frog carrying and delivering the eggs stuck.
How do the eggs survive on land for weeks?
The male keeps them from drying out and from being eaten. Frog spawn laid in a pond is exposed to fish, newts, insect larvae, fungus, and competition from other tadpoles, and spawn laid on land normally desiccates. By carrying the eggs on his body, the male midwife toad keeps them in a humid burrow by day, brings them to water at night to absorb moisture directly, and moves them away from any threat, and the eggs themselves are large and well provisioned. Only when the tadpoles inside are fully formed and ready to swim does he release them, so they spend the most vulnerable stage protected.
What was the Case of the Midwife Toad?
It was one of the most notorious episodes in the history of biology. In the 1900s and 1910s the Austrian biologist Paul Kammerer reported that if midwife toads, which mate on land, were forced to breed in water for several generations, the males developed dark, rough nuptial pads on their hands like water-breeding frogs, and that this trait was then inherited, which would support Lamarckian inheritance of acquired characteristics over Darwinian natural selection. In 1926 an examination of his last surviving preserved specimen showed the pad had been faked with injected India ink. Kammerer denied doing it, blamed an assistant, and shot himself weeks later. Whether he was a fraud, a victim of sabotage, or simply careless is still debated.
Are midwife toads endangered?
As a group, no, but individual species vary. The common midwife toad is still widespread across western Europe, though it has declined in the northern part of its range and in some countries. The species with small ranges are more at risk, and the standout case is the Majorcan midwife toad, which lives only in a few deep limestone gorges on that Balearic island. It was known first from fossils and believed extinct until a living population was discovered in 1980, and it is now heavily managed, with captive breeding, reintroduction, and efforts to keep the amphibian chytrid fungus out of its last streams.