Dogs and, less frequently, cats may be poisoned by oral exposure to many types of toads. Severity varies greatly, depending on extent of contact and type of toad. Toxins are produced by all toads, but potency varies with species and apparently between geographic locations within individual species. Toad toxin, a defensive mechanism, is secreted by large glands located dorsal and posterior to the eyes and by smaller glands distributed throughout the skin. The toxin, a thick, creamy white, highly irritating substance, can be expelled quickly by the contraction of periglandular muscles in the skin. Its many components include bufagenins, which have digitalis-like effects, and bufotoxins, which block sodium channels in nerves similar to the actions of local anesthetics, catecholamines, and serotonin. The most toxic species in the USA is the giant or marine toad, Rhinella marina (formerly Bufo marinus), an introduced species that is established in Florida, Hawaii, and Texas. R marina is also known as the cane toad in Australia, where its range extends across the northeastern half of the continent. Mortality ranges from 20%–100% in untreated cases, depending on exposure circumstances. The Colorado River toad, Incillus (formerly Bufo) alvarius, found in the southwestern USA and northern Mexico, is another toad of sufficient size to have potentially lethal levels of toxins in its skin secretions.