Strange Amphibians - Darwin's Frogs and Midwife Toads

Darwin’s frogs and midwife toads have unusual and fascinating methods of reproduction. In both of these amphibians the male plays an essential role in the development of the tadpoles. After the eggs of a Darwin’s frog have been laid and fertilized, the male guards them until the tadpoles - the first stage of the young frogs’ lives - move inside the eggs. The male then picks up the eggs with his tongue and places them in his vocal sac, which normally functions to amplify the male's sounds. Here the youngsters live and develop until they have become tiny froglets, at which point they leave the vocal sac to lead independent lives.

The female midwife toad lays a string of eggs. Once they are fertilized, the male midwife toad wraps the eggs around his hind legs and carries them around until the tadpoles are ready to be released from the eggs. The male takes his job very seriously, hiding in dark cavities except when he has to feed, and occasionally making trips to water to keep the eggs moist.

Darwin’s frogs live in Chile and Argentina and have the scientific name Rhinoderma darwinii. They’re named after Charles Darwin, the famous scientist who discovered the frogs by Chilean forest streams. The frog is a tiny creature and has a maximum size of about 3 cm, or 1.2 inches. It has a pointed snout and its upper surface is green or brown in color, or a mixture of the two colors. The frog’s lower surface is pale brown, and also has black and white patches. There is a ridge running down each side of the body.

Darwin's frogs are active during the day and spend most of their time on land in the leaf litter around forest streams and bogs. They feed mainly on insects but eat other small invertebrates too. Their coloration helps camouflage them against the leaf litter and protect them from predators.

Darwin's frogs often respond to danger by feigning death. They flip over on to their backs and stay still, on land or in water. They sometimes jump into the water to protect themselves, turning upside down to display their patterned underside and drifting in the water as though they are dead.

Darwin's frogs have a unique method of reproduction. The female deposits about forty eggs on the leaf litter. The female then leaves, but the male stays to fertilize and protect the eggs. After about three weeks the tadpoles are moving within the eggs that have survived. Just before they are ready to hatch the male picks the eggs up with his tongue and guides them through slits linking his mouth to his vocal sac. The male has a large vocal sac that can hold up to nineteen tadpoles and extends from his throat down his chest and on to his abdomen.

As the tadpoles develop they frequently move around, causing the vocal sac to ripple. They feed on yolk from the egg and on a secretion produced by the male. Metamorphosis, the process in which a tadpole changes into a frog, takes place inside the vocal sac. The froglets are able to leave the sac around six to eight weeks after the male picked up the eggs, and look like miniature versions of the adult. The male opens his mouth and the youngsters jump out.

The Darwin's frog population is classified in the "vulnerable" category of the IUCN Red List. This list, which is maintained by the International Union for Conservation of Nature, consists of seven categories denoting how close an animal population is to extinction.

In recent times another species of Darwin's frog, the Chile Darwin's frog (Rhinoderma rufum), existed in Chile. The IUCN Red List classifies this frog as critically endangered rather than extinct, but no members of the species have been seen since around 1980. In the Chile Darwin's frog the tadpoles are released from the male's vocal sac before they have changed into their adult form. The reasons for the frog's disappearance are uncertain, but habitat loss and disease may have played a role.

There are five species of midwife toads, all belonging the genus Alytes. (The genus is the first part of the scientific name.) The common midwife toad has the scientific name Alytes obstetricans and is native to countries in western and central Europe. The toad also lives in Britain, where it is an introduced species.

In general, a frog has moist, smooth skin and a toad had drier skin that is covered with warty bumps. Toads also have wider bodies and shorter legs than frogs, and they tend to walk instead of jump. These distinctions don’t always hold true, but they do apply to the midwife toad. This toad is brown or grey in color and its skin is covered by darker bumps. The underside is light grey or white. Midwife toads are small, but they are larger than Darwin’s frogs. They may reach 5.5 cm in length (2.2 inches).

Unlike the long, thin tongue of many other amphibians, the tongue of midwife toads is round and flattened. Midwife toads belong to a family called Discoglossidae, which also includes the painted frogs.

Midwife toads are nocturnal, spending their days in burrows or under logs or rocks. They spend most of their time on land, burrowing into the ground if they start to dry out. They feed on insects and small invertebrates like spiders, millipedes, worms and slugs. During winter the common midwife toad hibernates, usually in a burrow.

When a toad is alarmed, such as being by being attacked or handled, the "warts" on its skin produce a poison with a strong and unpleasant smell. This poison helps protect the toad from its predators. It doesn’t seem to affect humans, although it’s not a good idea for someone to touch their eyes right after handling a midwife toad.

The first midwife toad video in this hub includes the high pitched peeping sound made by the toad. It's often described as a ringing or bell-like call. A frog or toad makes sounds by moving air through the larynx, which is often called the voice box in humans. The common midwife toad has no vocal sac to amplify the sound, but its call is still very audible. During the breeding season the male calls to attract a female and she answers back.

During mating the male climbs on top of the female and wraps his front legs around her, a position known as amplexus. He also strokes her body with his back legs. These movements stimulate the female to release her eggs. The female catches the eggs between her back legs and the male fertilizes them. The fertilized eggs are then transferred to the male’s back legs.

There are about sixty eggs in a string. The male carries the eggs around for twenty to fifty days. If the weather is very dry he may dip the eggs into water to moisten them. The male may mate with more than one female and carry around more than one strand of eggs. When the eggs are ready to hatch the male enters the water. The tadpoles then emerge from the eggs and swim away.

Common midwife toad tadpoles grow to a very large size and become bigger than the adult. Unlike the adults, the tadpoles are vegetarians. After about eight months they change into the adult frog form.

The common midwife toad in classified in the "Least Concern" category of the IUCN Red List, but the other four species are classified in the "Vulnerable" or "Near Threatened" categories. These species include the Moroccan midwife toad, the Betic midwife toad in Spain, the Iberian midwife toad in Spain and Portugal and the Mallorca midwife toad in Majorca.

The Mallorca midwife toad, also called the Majorcan midwife toad (Alytes muletensis) is found in the wild only on the island of Majorca, where it lives in limestone gorges in remote areas. Before 1977 the species was thought to have been extinct for two thousand years, its population eliminated by introduced predators and competitors, but then researchers discovered living toads. The Durrell Zoo in Jersey has established a successful breeding program and repopulated wild areas with the toad. Other organizations are also involving in the Mallorcan midwife toad conservation program. In 1996 the toad was classified in the "Critically Endangered" Red List category, but in 2006 its population status was upgraded to the "Vulnerable" category.

Many fascinating and strange creatures belong to the amphibian group of animals. It would be a great shame to lose this diversity from Earth.