We lived in southern Arizona for 6 years. Insect pests troubled my garden and I know that spiders eat insects, so it seemed reasonable to introduce spiders into my garden. Not just any old spiders, what I had in mind were giant spiders, tarantulas, in fact. I figured big spiders would have big appetites and eat a lot of big insects.
In southern Arizona when the monsoon season starts in the summertime, tarantulas go on walk-about; literally thousands blacken the rural roads. I took a five gallon bucket and scooped up a bunch of the rascals, put a lid on the bucket, and when I got home, I dumped them in the garden to feast on insects.
Next morning I inspected the results, not a spider in sight! Apparently, they walked off in the night. I found one smashed in the street, but that was it.
Later, I learned why; it has to do with sex, procreation and all that stuff. It seems the females seldom venture more than a few feet from their underground burrow, but in mating season, they emit powerful pheromones. The males then go on walk-about in search of females. The guys I captured were all males looking for love, and my garden was the wrong place!