We stand in awe of the centuried Redwoods of the Pacific coast and the twisted, giant Saguaros of the high desert, but compared to the Chaparral bush they are mere infants.
The most famous successful example was the introduction of the gray moth, Cactoblastis cactorum, into Australia to control the prickly pear, Opuntia inermis, which was overrunning vast tracts of land.
Well, maybe you know what a cactus is. It's a, you know, the desert plant from Cowboy movies, and it has needles which stick and hurt and it's green, but yeah.
To be one of a crowd wandering around in search of a place to settle down, with your existence distilled down to a handful of mementoes and a cactus, is profoundly depressing.