You see, the tale is impossible. According to Dr. Clifford S. Crawford, professor of biology at the University of New Mexico, a tarantula might possibly lay eggs or build webs on, but not in, a cactus. Curators at the Desert Museum in Tucson, Arizona, point out that tarantulas live in burrows in the ground, especially the female, which rarely moves around on the surface. No tarantulas or spiders of any type ever have been known to burrow into plants, says Rod Crawford, curator of arachnids at the Burke Museum. Even if a small spider happened to climb into a hole in a cactus and lay eggs there, he says, the plant wouldn't explode when the eggs hatched.
Tarantulas take several years to reach full size.
Unlike the tarantula, a scorpion and her young might seek shelter within a cactus. It is therefore theoretically possible to find a scorpion lurking in a succulent. However, hatching scorpions aren't going to come flying out of a houseplant. A scorpion's pregnancy lasts up to a year and a half. Offspring are born live and then crawl onto their mother's back for another two to six weeks of external development.