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Bufo bufo, the common toad, is one of the most widely distributed amphibians in Europe. Its native range spans most of the continent, from Scandinavia south to North Africa and east through Russia into Kazakhstan, including Morocco, Algeria and Tunisia in North Africa and Lebanon at its eastern edge, though it is absent from Ireland and Iceland and from several Mediterranean islands. It is a large, robust toad: males reach up to about 8 cm in length, while females are larger, growing to about 10 cm.
Identification
The common toad’s colouring runs from brown to olive-brown, though it is a variable species, and females are often reddish or carry reddish warts. The skin is warty and typically dry, which separates the common toad at a glance from the smoother, moister skin of frogs sharing the same ponds. Behind this rough surface sit glands that contain powerful toxins, a chemical defence unpalatable to most predators; the tadpoles carry the same toxins in their skin, so the species is protected from egg to adult.
Habitat and range
Within its wide native range, the common toad is widespread across mainland Britain and many of its islands, including the Isle of Wight, but absent from Ireland. For breeding, it favours deeper standing water, such as farm ponds, reservoirs, fish ponds and village duck ponds, and adults show a strong migratory instinct, returning to the same ancestral pond each spring. Outside the breeding season the common toad is more tolerant of dry conditions than the common frog, and it ranges widely into gardens and other dry ground through the summer months, often settling in one spot for as long as food remains plentiful there.
Well outside this native range, the species was also stocked on Kauai, Hawaii, as a biocontrol agent, with records running from 1933 to 1953; the surveying agency notes that population may no longer be present today.
Behaviour and breeding
Common toads are largely nocturnal hunters, taking ants, beetles, snails, slugs and spiders after dark. Each spring they migrate back to their breeding ponds, arriving a couple of weeks after the common frog. Mating pairs form in amplexus, and the toad’s spawn is distinctive: toadspawn is laid in strings, not clumps like a frog’s. The tadpoles that hatch are also easy to tell apart from a frog’s: common toad tadpoles are black and gather in shoals, rather than dispersing individually.
Conservation
The IUCN category for the common toad is given in the facts box above. Locally, though, the picture is less settled: in Britain the species is protected only from sale and trade, and has been listed as a biodiversity priority species under the NERC Act 2006 in response to recent population declines, tied in part to the loss of the deeper ponds it needs for breeding. A species can carry a secure global category while individual populations quietly disappear from ponds that no longer suit them.
Similar species
The common toad shares much of its range and many of its breeding ponds with the common frog, and the two are frequently confused. Skin is the fastest check: the toad’s warty, typically dry texture contrasts with the frog’s smooth, moist skin, and the toad also moves with a slow crawl rather than the frog’s bounding hop. In the water, the spawn tells them apart at once — strings from the toad against clumps from the frog — and so do the tadpoles, with the common toad’s black, shoaling tadpoles standing apart from the paler, speckled tadpoles of the common frog. Where a garden pond is visited by both species, these traits, rather than colour alone, are the reliable way to tell the common toad from its more familiar cousin.
Further afield, the common toad also has a close look-alike in its own genus: the Jersey toad, Bufo spinosus, found on the Channel Islands in place of Bufo bufo, is similar enough in build and colouring that the two are best told apart by range rather than by eye.