The story about an ornamental cactus releasing spiders is a popular myth.
Such an event is particularly unlikely to involve tarantulas, which might possibly lay eggs or build webs on, but not in, a cactus plant.
Tarantulas live in burrows in the ground, especially the female, which rarely moves around on the surface. Tarantulas take several years to reach full size.
The “spiders in the cactus” story, almost invariably heard about a friend of a friend, is one of the most persistent of urban myths.
The story is often attached to the name of a well-known dealer or store.
The cactus in question is supposed to have been field-grown or harvested wild in the desert.
It starts to tremble, the story goes, and then releases its awful contents: spiders or scorpions. Sometimes the victim is said to call the dealer, who sends men with a plastic bag, just in time.
However, there is apparently no verifiable instance of this having happened, and commercially sold cactuses are almost always raised in a controlled environment.
Tarantulas also have an undeserveclly bad reputation.
Tarantulas are very docile animals and are not easily provoked to bite. The usual prey of Phechostica chalcodes, the most common species in Arizona, is insects.
Its fangs are seldom used on humans and do not cause any serious complications.
A Mexican variety is even sold as a pet.