Why Are Spiders Beneficial?
S. E. Riechert and L. Bishop of the University of Tennessee found that spiders were good general predators in home gardens and generally in the home landscape. Mixed vegetable gardens with spinach, tomato, bean, broccoli, potato and corn had large spider populations. Using hay mulch increased the number of spiders and, with this increase, there were fewer pests and less plant damage. Flowers had no significant effect on the spider population, but this is not bad. Spiders are still in the flowers. Turfgrass that is cut no lower than two inches and is very dense (as dense as new sod) will also serve as habitat for an enormous number of spiders in every 1000 square feet.
Spiders will dine on aphids, boll weevils, armyworm, leafhoppers, fleahoppers, leafminers and spider mites. They will attack the spruce budworm, pine sawfly, sorghum midge and the tobacco budworm. Spiders also enjoy virtually all caterpillars, thrips, plant bugs, cucumber beetles, grass-hoppers, scarabs and flies. In the lawn they go after the eggs and larvae of sod webworm, chinch bug, and the billbug.
According to W.S. Bristowe, a British authority on spiders, these good guys consume far more insects than birds do. Better yet, the spiders will eat almost everything caught in their web. This makes the spider a splendid generalist as opposed to many beneficials that specialize in their din-ing habits.
Even where spiders do not kill and or eat all the pest insects in a given area, there are certain pest species that flee an area where spiders are present. The greenbug, leaf fly and leafhoppers are three species that flee when spiders are present.
Worldwide, spiders eat enough insects in one year to equal the weight of the entire human population.