6 - Impact of spiders on insect populations

Summary

Spider stories

Spiders evoke ambivalent responses. Many who find spiders frightful reluctantly recognize their good in a world populated by alarming numbers of equally repulsive insects. Popular wisdom attributes miraculous powers to spiders as decimators of insect populations (Bristowe 1971):

If you wish to live and thrive

Let a spider run alive.

Or, for those who insist on translating their ecological intuition into precise interaction coefficients:

Kill a spider, bad luck yours will be

Until of flies you've swatted fifty-three.

Folk wisdom must have some basis in fact, springing as it does from uncounted generations of practical naturalists who have watched spiders capture insect pests. Mexicans bring colonies of the social spider Mallos gregalis into their homes to use as fly paper during the rainy season; this species is known as ‘el mosquero,’ the fly killer (Burgess 1976). The giant crab spider Heteropoda venatoria (Sparassidae) is a common house spider that occurs world-wide in tropical regions (Gertsch 1979). A nighttime marauder who hides during the day, H. venatoria usually is welcome because of its fondness for cockroaches and other creatures active after dark. H. venatoria is common in parts of Florida, where a survey of households yielded the surprising result that over half of the respondents were willing to introduce this impressively large arachnid into their homes to control cockroaches (Trambarulo 1981). Residents of more temperate regions, unaccustomed to the exuberance of the tropical fauna, might have been more reluctant, though they do tolerate the drab house spiders that spin traps in cellar corners.