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Toads

Biology Of Toads

Toads are amphibious animals, breeding in water, but able to use terrestrial habitats as adults. As adults, toads potentially can live a long time. One of the longest-lived toads was a European common toad (Bufo bufo), which survived for 36 years in captivity.

Toads have a complex life cycle, similar to that of frogs. Toads lay their eggs in water, typically inside of long, intertwined strings of a gelatinous material (toad spawn). The eggs hatch into small, dark-colored aquatic larvae (called tadpoles) which have a large head that is not distinctly separated from the rest of the body, internal gills, and a large, flattened tail which undulates side-ways to achieve locomotion. Toad larvae are herbivores that feed on algae, bacteria, and other materials occurring on the surface of vegetation, stones, and sediment.

The larval stage ends with a metamorphosis into the adult life form. Adult toads are characterized by internal lungs used for the exchange of respiratory gases, a tailless body, a pelvis that is fused with many of the vertebra to form a bulky structure known as the urostyle, large hind legs adapted for hopping and walking, and small forelegs used to achieve stability, and to help with eating by feeding certain types of prey, such as long earthworms, into the mouth. Adult toads also have a relatively thick, dry skin that is heavily cornified with the protein keratin, and provides these terrestrial animals with some degree of protection against dehydration and abrasion. Adult toads are exclusively carnivorous, feeding on a wide range of invertebrates and other small animals.

During the breeding season, toads congregate in their breeding ponds, sometimes in large numbers. The males have species-specific songs that are used to attract females. The vocalizations range from long, trilling songs, to shorter, barking sounds. Singing is enhanced by the inflatable vocal sac of male toads, which amplifies their sounds by serving as a resonance chamber. Mating involves the male sitting atop the female in amplexus, gripping tightly using his forelegs, and fertilizing the ova as they are laid by the female. Once laid, the eggs are abandoned to develop by themselves.

Toads are very fertile. As many as 30,000 eggs may be laid by the cane toad (Bufo marinus), and even the much smaller American toad (B. americanus) may lay as many as 25,000 eggs.

The skin of all amphibians contains glands that secrete toxic chemicals, used to deter predators. These glands are quite large and well developed in the warty skin of adult toads, especially in the paired structures at the sides of the head, known as the parotoid glands. In large toads, such as the cane toad, the quantity and toxicity of the contained poison is sufficient to kill a naive, large predator that foolishly takes a toad into its mouth.

Although toads are relatively resistant to dehydration, they are by no means immune to this stress. Adult toads tend to stay in a cool, moist, secluded place during the day, emerging to feed at night when the risk of dehydration is less. When the opportunity arises, toads will sit in a pool of water to rehydrate their body.

Adult toads use their tongues when feeding. The tongue is attached near the front of the mouth, and can be flipped forward to use its sticky surface to catch a prey animal, which is then retrieved into the mouth. This method of feeding is known as the "lingual flip," a maneuver that can be executed in less than 0.2 seconds, and is especially useful for capturing relative small, flying prey, such as insects.

Toads will attempt to eat any moving object of the right size. However, some prey are considered distasteful by toads, and are spat out.


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Science EncyclopediaScience & Philosophy: Thallophyta to ToxicologyToads - Biology Of Toads, Toads Of North America, Toads And Humans