Alytes obstetricans (Common Midwife Toad): identification, habitat and breeding

Alytes obstetricans, the common midwife toad, is a small, stocky toad of the family Alytidae, native to France, Belgium, the Netherlands, Luxembourg, western Germany, northern and western Switzerland, Portugal and northern Spain. It takes its common name from an unusual piece of parental care found in no other European amphibian: the male carries the fertilised eggs entwined on his back and thighs until they are ready to hatch.

Identification

The toad is broad and stocky, growing to a maximum length of about 55 mm, with females generally larger than males; most adults found in the field are smaller than that maximum. It has a large head with prominent eyes and vertical, slit-shaped pupils, a trait that separates it at a glance from Europe’s round-pupilled true toads. The skin is mostly smooth with small warts and granules, including a row of larger warts running down each side, plus small parotoid glands and extra glands under the arms and around the ankles, and each front foot carries three small tubercles on the underside of the hand. Colouring is highly variable — grey, olive or brown, often with greenish or brown spotting, and warts that are typically reddish or yellow; the underside is pale grey with darker spots on the throat and chest. When threatened, it may inflate its body, rear up on all four limbs and raise its rump with its head down and eyes shut, a defensive posture rather than a bite or toxin.

Habitat and range

The species favours hilly and cultivated land, quarries, rocky slopes, gravel pits, woods, parks and gardens, typically staying near water but sometimes ranging up to 500 m away, and in the Pyrenees it climbs to about 2,400 m altitude. By day it shelters in damp refuges such as undergrowth, crevices, or under logs and stones, and it hibernates on land rather than in water. Its native range runs across France, Belgium, the Netherlands, Luxembourg, western Germany, northern and western Switzerland, with disconnected populations in Portugal and northern Spain; it has also been introduced to Britain, where small founder populations have shown limb deformities.

Behaviour and breeding

The toad feeds mostly on insects and other arthropods, as well as carrion. Its breeding behaviour is what gives the species its name: after mating on land, the male winds the string of fertilised eggs around his hind legs and back and carries them for three to eight weeks until they are ready to hatch. A single male can carry up to three clutches at once, roughly 150 eggs in total, keeping them moist by resting in damp shelters and periodically dipping into water. When the eggs are close to hatching he enters calm water — a ditch, pond, spring, trough or even a flowerpot saucer — and releases the tadpoles, which then take several months to metamorphose, sometimes overwintering as unusually large tadpoles before completing their development the following year. Unlike most European frogs and toads, courtship and egg-laying happen entirely on land, and the water is used only for the tadpole stage that follows.

Conservation

The IUCN category is shown in the facts box above. The main pressure on the species is habitat loss rather than any single acute threat. Britain’s introduced populations show a different risk: there, limb deformities have been linked to the small size of the founding population.

Similar species

Alytes obstetricans belongs to a small genus of five living species, all sharing the male’s egg-carrying habit but replacing one another geographically. The Iberian midwife toad, Alytes cisternasii, occupies Portugal and western Spain; the Betic midwife toad, Alytes dickhilleni, is restricted to south-eastern Spain; the Moroccan midwife toad, Alytes maurus, is found only in Morocco; and the Mallorcan midwife toad, Alytes muletensis, survives only on the Balearic island of Mallorca, where it has evolved a flatter body that lets it squeeze into narrow rock crevices and breeds in rain-filled rock pools rather than ponds. Within Alytes obstetricans itself, genetic evidence suggests that one of its four subspecies, Alytes obstetricans almogavarii, may deserve recognition as a separate species, so the group’s boundaries are still being worked out. None of its relatives overlap with the common midwife toad’s own range, so any egg-carrying Alytes seen in France, the Low Countries, western Germany or Switzerland can be identified as this species by range alone.