The common toad, European toad, or in Anglophone parts of Europe, simply the toad (Bufo bufo, from Latin bufo "toad"), is an amphibian found throughout most of Europe (with the exception of Ireland, Iceland, and some Mediterranean islands), in the western part of North Asia, and in a small portion of Northwest Africa. It is one of a group of closely related animals that are descended from a common ancestral line of toads and which form a species complex. The toad is an inconspicuous animal as it usually lies hidden during the day. It becomes active at dusk and spends the night hunting for the invertebrates on which it feeds. It moves with a slow, ungainly walk or short jumps, and has greyish-brown skin covered with wart-like lumps.
Description & appearance
The common toad can reach about 15 cm (6 in) in length. Females are normally stouter than males and southern specimens tend to be larger than northern ones. The head is broad with a wide mouth below the terminal snout which has two small nostrils. There are no teeth. The bulbous, protruding eyes have yellow or copper coloured irises and horizontal slit-shaped pupils. Just behind the eyes are two bulging regions, the paratoid glands, which are positioned obliquely. They contain a noxious substance, bufotoxin, which is used to deter potential predators. The head joins the body without a noticeable neck and there is no external vocal sac. The body is broad and squat and positioned close to the ground. The fore limbs are short with the toes of the fore feet turning inwards. At breeding time, the male develops nuptial pads on the first three fingers.
He uses these to grasp the female when mating. The hind legs are short relative to other frogs' legs and the hind feet have long, unwebbed toes. There is no tail. The skin is dry and covered with small wart-like lumps. The colour is a fairly uniform shade of brown, olive-brown or greyish-brown, sometimes partly blotched or banded with a darker shade. The common toad tends to be sexually dimorphic with the females being browner and the males greyer. The underside is a dirty white speckled with grey and black patches.
Other species with which the common toad could be confused include the natterjack toad (Bufo calamita) and the European green toad (Bufo viridis). The former is usually smaller and has a yellow band running down its back while the latter has a distinctive mottled pattern. The paratoid glands of both are parallel rather than slanting as in the common toad. The common frog (Rana temporaria) is also similar in appearance but it has a less rounded snout, damp smooth skin, and usually moves by leaping.
Common toads can live for many years and have survived for fifty years in captivity. In the wild, common toads are thought to live for about ten to twelve years. Their age can be determined by counting the number of annual growth rings in the bones of their phalanges.
Common toads winter in various holes in the ground, sometimes in basements, often in droves with other amphibians. Rarely they spend the winter in flowing waters with the common frogs and green frogs.
Distribution & habitat
After the common frog (Rana temporaria), the edible frog (Pelophylax esculentus) and the smooth newt (Lissotriton vulgaris), the common toad is the fourth most common amphibian in Europe. It is found throughout the continent with the exception of Iceland, the cold northern parts of Scandinavia, Ireland and a number of Mediterranean islands. These include Malta, Crete, Corsica, Sardinia and the Balearic Islands. Its easterly range extends to Irkutsk in Siberia and its southerly range includes parts of northwestern Africa in the northern mountain ranges of Morocco, Algeria and Tunisia. A closely related variant lives in eastern Asia including Japan. The common toad is found at altitudes of up to 2,500 metres (8,200 ft) in the southern part of its range. It is largely found in forested areas with coniferous, deciduous and mixed woodland, especially in wet locations. It also inhabits open countryside, fields, copses, parks and gardens, and often occurs in dry areas well away from standing water. Food
The common toad usually moves by walking rather slowly or in short shuffling jumps involving all four legs. It spends the day concealed in a lair that it has hollowed out under foliage or beneath a root or a stone where its colouring makes it inconspicuous. It emerges at dusk and may travel some distance in the dark while hunting. It is most active in wet weather. By morning it has returned to its base and may occupy the same place for several months. It is voracious and eats woodlice, slugs, beetles, caterpillars, flies, earthworms and even small mice. Small, fast moving prey may be caught by a flick of the tongue while larger items are grabbed with the jaws. Having no teeth, it swallows food whole in a series of gulps. It does not recognise its prey as such but will try to consume any small, dark coloured, moving object it encounters at night. A research study showed that it would snap at a moving 1 cm (0.4 in) piece of black paper as if it were prey but would disregard a larger moving piece. Toads seem to use visual cues for feeding and can see their prey at low light intensities where humans are unable to discern anything. Periodically, the common toad sheds its skin. This comes away in tattered pieces and is then consumed.
When attacked, the common toad adopts a characteristic stance, inflating its body and standing with its hindquarters raised and its head lowered. Its chief means of defence lies in the foul tasting secretion that is produced by its paratoid glands and other glands on its skin. This contains a toxin called bufagin and is enough to deter many predators although grass snakes seem to be unaffected by it. Other predators of adult toads include hedgehogs, rats and mink, and even domestic cats. Birds that feed on toads include herons, crows and birds of prey. Crows have been observed to puncture the skin with their beak and then peck out the animal's liver, thus avoiding the toxin. The tadpoles also exude noxious substances which deter fishes from eating them but not the great crested newt. Aquatic invertebrates that feed on toad tadpoles include dragonfly larvae, diving beetles and water boatmen. These usually avoid the noxious secretion by puncturing the tadpole's skin and sucking out its juices. Mating & reproduction
The common toad emerges from hibernation in spring and there is a mass migration towards the breeding sites. The toads converge on certain ponds that they favour while avoiding other stretches of water that seem eminently suitable. Adults use the same location year after year and over 80% of males marked as juveniles have been found to return to the pond at which they were spawned. They find their way to these by using a suite of orientation cues, including olfactory and magnetic cues, but also visual cues help guide their journeys. Toads experimentally moved elsewhere and fitted with tracking devices have been found to be able to locate their chosen breeding pond when the displacement exceeded three kilometres (two miles).
The males arrive first and remain in the location for several weeks while the females only stay long enough to mate and spawn. Rather than fighting for the right to mate with a female, male toads may settle disputes by means of the pitch of their voice. Croaking provides a reliable sign of body size and hence of prowess. Nevertheless, fights occur in some instances. In a study at one pond where males outnumbered females by four or five to one, it was found that 38% of the males won the right to mate by defeating rivals in combat or by displacing other males already mounted on females. Male toads generally outnumber female toads at breeding ponds. A Swedish study found that female mortality was higher than that of males and that 41% of females did not come to the breeding pond in the spring and missed a year before reproducing again.
The males mount the females' backs, grasping them with their fore limbs under the armpits in a grip that is known as amplexus. The males are enthusiastic, will try to grasp fish or inanimate objects and often mount the backs of other males. Sometimes several toads form a heap, each male trying to grasp the female at the base. It is a stressful period and mortality is high among breeding toads. A successful male stays in amplexus for several days and, as the female lays a long, double string of small black eggs, he fertilises them with his sperm. As the pair wander piggyback around the shallow edges of the pond, the gelatinous egg strings, which may contain 3000 to 6000 eggs and be 3 to 4.5 metres (10 to 15 ft) in length, get tangled in plant stalks.
The strings of eggs absorb water and swell in size, and small tadpoles hatch out after two to three weeks. At first they cling to the remains of the strings and feed on the jelly. They later attach themselves to the underside of the leaves of water weed before becoming free swimming. The tadpoles at first look similar to those of the common frog (Rana temporaria) but they are a darker colour, being blackish above and dark grey below. They can be distinguished from the tadpoles of other species by the fact that the mouth is the same width as the space between the eyes, and this is twice as large as the distance between the nostrils. Over the course of a few weeks their legs develop and their tail gradually gets reabsorbed. By twelve weeks of age they are miniature toads measuring about 1.5 cm (0.6 in) long and ready to leave the pond.
The common toad reaches maturity at three to seven years old but there is great variability between populations. Juveniles are often parasitised by the lung nematode Rhabdias bufonis. This slows growth rates and reduces stamina and fitness. Larger juveniles at metamorphosis always outgrow smaller ones that have been reared in more crowded ponds. Even when they have heavy worm burdens, large juveniles grow faster than smaller individuals with light worm burdens. After several months of heavy worm infection, some juveniles in a study were only half as heavy as control juveniles. Their parasite-induced anorexia caused a decrease in food intake and some died. Another study investigated whether the use of nitrogenous fertilisers affects the development of common toad tadpoles. The toadlets were kept in dilute solutions of ammonium nitrate of various strengths. It was found that at certain concentrations, which were well above any normally found in the field, growth was increased and metamorphosis accelerated, but at others, there was no significant difference between the experimental tadpoles and controls. Nevertheless, certain unusual swimming patterns and a few deformities were found among the experimental animals.
A comparison was made between the growth rate of newly metamorphosed juveniles from different altitudes and latitudes, the specimens studied being from Norway, Germany, Switzerland, the Netherlands and France. At first the growth rates for males and females was identical. By the time they became mature their growth rate had slowed down to about 21% of the initial rate and they had reached 95% of their expected adult size. Some females that were on a biennial breeding cycle carried on growing rapidly for a longer time. Adjusting for differences in temperature and the length of the growing season, the toads grew and matured at much the same rate from the four colder localities. These juveniles reached maturity after 1.09 years for males and 1.55 years for females. However, the young toads from lowland France grew faster and longer to a much greater size taking an average 1.77 years for males and 2.49 years for females before reaching maturity.