Toads belong to the order Anura of the class Amphibia. The name toad is restricted to the so-called ‘true toads’ of the family Bufonidae. The European common toad is classified as Bufo bufo.
Toads are froglike amphibians that can usually be distinguished from frogs by their drier and rougher skins, often described as ‘warty’ in appearance, due to a large number of glandular tubercules. They have shorter hind legs, a flatter head, swollen parotid glands on the side of the neck behind the eyes and slightly webbed toes.
The common toad has a rough, usually dark-brown skin in which there are glands secreting a poisonous fluid that makes it unattractive as food for other animals. It needs this protection because it has an ungainly crawl which makes it’s progress slow. European toads have a size range of 2- 25cm.
Toads are shy, usually nocturnal animals that live mostly on land, hiding during the day in dark, damp places and becoming active at night in search of insects, grubs, slugs, worms, and other invertebrates. Adults are completely carnivorous and respond only to moving prey. Anything that is small enough to be swallowed will be considered as long as its movement is not too fast. When threatened by a predator, the common toad reacts by raising itself up on all fours and inflating itself to give the appearance of being much larger than it actually is, then moves straight towards the predator as if to charge with its head.
In temperate regions, toads hibernate over the winter months in burrows. In the early spring in response to hormonal changes stimulated by temperature and moisture, sexually mature adults migrate, often traveling large distances from their land sites to suitable breeding waters. Areas where traces of amphibian activity is low for much of the year will suddenly become alive with activity, with the sexually mature adults representing only a percentage of the total amphibian population. After mating the toads return to their summer habitats where they may burrow and remain inactive until temperatures rise above 10-12oC. In the autumn a less conspicuous migration takes place as the toads leave their summer habitats and return to their winter hibernation sites.
Toads which are usually shy and secretive animals come out in mass during the mating season and congregate at their breeding ponds, often returning to the same grounds in which they were spawned. Males first breed from two to three years of age and females from three to six years of age. To successfully breed both sexes have to be present at the right time and be able to find each other. This is achieved by a complex behavioural pattern, a process that most senses play a part in. Toads react to many odours including pheromones, light, temperature and moisture. Their hearing becomes very sensitive to different pitches, atmospheric pressures and vibrations that make up the male mating call. The tactile senses on the toes and the underside of males become well developed as does the back of the females.
When two individuals come together, the male will try to grasp the other. If it is another male, or a female that has already mated or is not yet ready to mate, then a defensive posture will be adopted. If the two are compatible then the result is the mating embrace or amplexus, during which the male will ward of others by kicking with its hind legs. Fertilization is external, with the male fertilizing the eggs as they are laid. The male releases a single spermatophore approximately 5mm in length that is picked up by the female through her cloaca. Once fertilised the females lay their spawn in water. The numerous ova are attached to rocks or vegetation and laid in double gelatinous strings up to 4.6m (15 ft) in length. The tadpoles hatch after 10-21 days and are smaller and darker than those of frogs. The toadlets leave the water during the warm humid conditions of summer, completing their transformation into terrestrial toads in the autumn.
1: Toad Spawn
2-3: Developing ova
4-5: Tadpoles with external gills
6-7: Development of rear limbs
8-9: Development of front limbs
10: Metamorphosis to a toad