Common Toad

Family: Bufonidae - True Toads

Order: Anura - Frogs and Toads

Class: Anura

Phylum: Chordata - Vertebrates

Kingdom: Animalia

Red List status: Least Concern

Bufo bufo (Linnaeus, 1758)
Common toad, breeding male. Epping Forest, Essex, United Kingdom

Adult length

Male: 65-82 mm

Female: 80-95 mm, exceptionally to 150 mm

 

Metamorph length: 7-12 mm

Tadpole length: 26 mm

RANGE

Mainland Europe to western Asia and north-west Africa. Common toads are generally absent from islands, but are widespread in Great Britain.

DESCRIPTION

Adult: A large, very robust toad with distinctly warty skin, thickset limbs and eyes with horizontal pupils, and with no external vocal sac. The parotid glands are obvious, oval and at a slightly oblique angle, rather than parallel to one another. The body is unpatterned or with dark patches. Colouration is usually dark brown, although shades vary and ground colouration ranges from grey to olive. Red or orange markings may be present on some warts of females and juveniles. The forearm is especially heavy in breeding males, which also exhibit large nuptial pads on the thumb. The venter is pale, typically with brown mottling. The iris is gold, with black veining. The tympanum is visible. There is generally a pair of tubercles beneath the longest hind toe.

 

Call: The mating call is quiet and slow, with long croak-like notes, and is not often heard. Male toads often emit a high-pitched

squeak as a release call if grabbed in amplexus by another male.

Common toad underside and iris details.

Tadpole: Tadpoles are small and blackish, darker than tadpoles of the common frog (Rana temporaria). Larvae often aggregate in large clusters at the water surface, often near the centre of the waterbody.

Eggs: Eggs are laid in a string that females drape around submerged vegetation; this may be up to 5 m long and can contain up to 4,000 eggs. Fenales lay two strings simultaneously, resulting in a double-stranded structure that allows eggs to be distinguished from the single-stranded egg masses of natterjacks. However, this character needs to be interpreted with caution as common toad eggs may be stretched into a single strand. Natterjack eggs are never double-stranded.

Similar species: Only three other European species possess parotid glands. Only the common and Caucasian toads have oblique paratoid glands; those of natterjack and green toads are roughly parallel. These species are smaller, and also have external vocal sacs, and a single tubercle beneath the longest hind toe. The natterjack (Epidalea calamita) almost invariably possesses a thin, yellow mid-dorsal line, never present in the common toad. Both this and the green toad have paler yellow rather than gold eyes. The green toad (Pseudepidalea viridis) is strongly patterned in with green blotches over a pale surface. Spadefoot toads also have warty skins and similar undersides, but has no visible tympanum. The Caucasian toad (B. verucosissimus) is larger, sandy or reddish in colour, and is mostly known from mountainous areas and conifer forest. The tongue shape of this species is reported to differ from that of B. bufo.

 

HABITAT

Common toads are more fully terrestrial than many European amphibians, spending more than 90% of their time on land. Animals are active at night, spending the day sheltering in retreat sites, typically cover objects such as fallen logs or rocks. Animals will often reuse these sites, returning to a favoured spot from as far as 250 metres. Rarely, animals will bask in daylight for short periods or forage in the day following rain. Common toads occur in a wide variety of terrestrial habitats throughout their range, often in rather dry areas..

Reproductive habitat: Toads breed in standing water, preferring large, permanent ponds where their larvae can develop without risk of desiccation, although deep ditches may be used. An optimal waterbody is around 1,000 m2 in area. As toad eggs and tadpoles are toxic to predators, this species will often make use of habitats occupied by fish.

Elevation: 0-3,000 m

 

BEHAVIOUR

Toads are incapable of jumping; instead, in contrast to most frogs, they walk or hop short distances. They are strong climbers. Toads are migratory, with animals returning to favoured breeding sites from the surrounding countryside in large numbers. The peak migration period occurs in spring as animals emerge from hibernation, during March and April in Britain, although individual animals may begin migration several months earlier. Males typically reach the breeding pond first and await the arrival of females. The hibernation period itself may start as early as October, and animals will dig burrows or make use of existing mammal burrows as hibernation sites.

Reproductive behaviour: Common toads are an extreme example of an explosive-breeding species; animals may spend no more than two or three nights in water during the breeding season; during these periods animals are extremely active, with males forming large aggregations in and around the breeding site. Toads are notoriously amorous in their courtship, with males forming 'mating balls' of up to a dozen animals grasping individual females. Animals often drown or die from stress during this process. Although males have a soft mating call, they will often physically fight for access to females. Toads may grasp fish, male frogs or inanimate objects in amplexus. Females lay egg strings around vegetation in exposed areas of the pond, often over a period of several hours.

Defensive behaviour: As a response to potential predators, toads raise themselves up on their hindlimbs and inflate their bodies to make themselves appear larger than they are. As with other true toads, they can also exude a latex-like substance from the parotid glands which is toxic to predators.

Diet: Varied, including earthworms, snails, insects and occasionally small vertebrates. Toads may actively pursue prey animals for several minutes; and may use their forelimbs to manoeuvre prey into the throat.

 

BIOLOGY

Life cycle: The egg stage in this species lasts for 2-3 weeks. Tadpoles metamorphose after a larval stage lasting around two months. Common toads reach sexual maturity at 3-7 years in northern parts of their range. In contrast to common frogs, toad tadpoles are unable to accelerate their development in response to reductions in water level over the course of the summer, hence the females' preference for larger, more permanent waterbodies as breeding sites.

Lifespan: Toads are relatively long-lived amphibians, with captive specimens living for over 40 years. In the wild, animals are known to live to the age of 10.

 

STATUS

Common toad populations are thought to be stable in most of the species' range; however, populations are threatened within localised areas. In central Spain, mass mortality of common toads due to chytrid fungus has been reported. The British population is increasingly recognised as being under threat; many animals are killed annually on roads as they migrate to breeding sites, leading to volunteer efforts to move animals safely across roads at designated Toad Patrol sites administered by the amphibian and reptile charity Froglife. Much of the British decline is, however, due to unknown causes, which may include the effects of climate change.

 

TAXONOMY

Bufo bufo represents a complex of several species, although the taxonomy of this group is unclear. Subspecies have been defined in the Mediterranean and the Sierra de Gredos region of central Spain. The Spanish form, B. b. gredosicola, possesses very large parotid glands, while the Mediterranean B. b. spinosus is a large form with spiny skin. A former subspecies, B. verrucosissimmus, was recently elevated to full species status.

 

REFERENCES

Arnold, N. and Ovenden, D. (2004) Collins Field Guide: Reptiles and Amphibians of Britain and Europe HarperCollins, London: 288pp

Beja, P., Kuzmin, S., Papenfuss, T., Stöck, M., Denoël, M., Sparreboom, M., Ugurtas, I., Ishchenko, V., Tuniyev, B., Anderson, S., Beebee, T.,  Andreone, F., Nyström, P., Anthony, B. and Schmidt, B. (2006). Bufo bufo. In: IUCN 2008. 2008 IUCN Red List of Threatened Species.

Jarvis, L. Advanced British Amphibians Field Studies Council course, Epping Forest, Essex.

Wareham, D.C. (2008) The Reptiles and Amphibians of Dorset British Herpetological Society: 120pp

Range            Description            Habitat            Behaviour            Biology            Status            Taxonomy            References

Bufo bufo, breeding male. Note the heavily thickened forelimb and the angle of the parotid gland.