The animal at the center of these stories is most likely Bufo Alvarius, commonly called the Sonoran Desert Toad or the Colorado River Toad. These are big toads with adults varying from 4 to 7.5 inches in length, and they can be found in the southern half of Arizona as well as Imperial County, California; Hildalgo County, New Mexico; and parts of northwestern Mexico (Sonora and northern Sinaloa states). Bufo Alvarius is carnivorous (eating mostly insects and some smaller rodents and reptiles) and nocturnal. They are most commonly spotted after summer rains at night or in the early morning hours.
As a defense mechanism to protect itself from predators, this toad has glands which secrete a number of toxins including 5-MeO-DMT (a psychoactive chemical also found in a number of plants including the ayahausca vine) and bufotenin (which is similar to psilocin, a chemical present in psychoactive mushrooms, and DMT). On average, 5-MeO-DMT may represent around 15% of the venom's dry weight.
Why you shouldn't lick toads
There's two very good reasons why no one who knows what he is doing would lick these animals: (1) apparently you cannot experience the psychotropic effects of bufotenin by ingesting the substance, and – much more importantly – (2) ingesting all the toxins present in the toad's venom can make you very sick and might even be fatal.
This is a big problem for dog owners living in the Sonoran Desert Toad's natural range given that dogs have a habit of licking things and putting them in their mouth. Symptoms of toad poisoning include vomiting, numbing/paralysis, difficulty breathing and heart arrythmia, and it is possible for a single toad to produce enough poison to kill a large dog. Owners who see their dog playing around with one of these toads are advised to rinse out the dog's mouth with a hose and to contact a vet if they notice any symptoms of poisoning.
Myths about human toad licking probably arose from sensational media stories reporting on a false trend among hippies or drug users who were supposedly licking toads to get high in significant numbers. Like many a bad trend story, these were no doubt based on rumors, incomplete evidence, and isolated incidents.
Smoking toad venom
So people in the know don't really lick toads to get high, but people have tried milking Sonoran Desert Toads for their venom and smoking it. This apparently allows one to experience the full psychotropic power of the chemicals present in the toad's venom while avoiding the ill effects that results from ingesting it.
An infamous 1983 pamphlet explains the process in detail: basically, you pick up one of these toads in one hand and with the other squeeze the glands located behind its eyes and on its legs so the toxin squirts onto a plate of glass. Wait an hour and repeat the process. Then you allow the venom to dry, scrape it off the glass, chop it up into a powder, put it in your pipe and smoke it. Once a toad is fully drained of venom, it takes 4-6 weeks for it to replenish its stock.
According to the pamphlet, with the right dose a smoker will experience 2-3 minutes of intense psychodelic effects followed by another 12 minutes of LSD-like experiences. After that one might experience several hours of "afterglow" in which one experiences diminished psychodelic sensations. The pamphlet's author lists the short duration of the psychodelic experience and the absense of any type of hangover among the advantages to smoking dried toad venom.
The law and Bufo Alvarius
Bufotenin, one of the chemicals present in bufo alvarius' venom, is listed as a Schedule I controlled substance in the US (no accepted medical use, high potential for abuse), and thus possession is a federal offense.
Occasionally, people have been arrested for possessing a Sonoran Desert Toad with the intent of harvesting its venom for drug use, but it is apparently perfectly legal to keep bufo alvarius for innocent purposes (i.e. pet toad). They may even be available at some pet stores (which seems INSANE given their toxicity). At any rate, I'd think prosecuting owners of Sonoran Desert Toads would be anything but straightforward if prosecutors have to prove that they were specifically kept for drug purposes.
As for catching bufo alvarius, this species is listed as threatened in New Mexico and as a species of special concern (possibly extinct) in California so it is illegal to take them from the wild. In Arizona, where they are more plentiful, there are laws restricting the removal of any wildlife from the state.
Image: photo of bufo alvarius by California Academy of Sciences.