Spider fauna was sampled in 1983 and 1984 from action sites of adult European corn borer (ECB),Ostrinia nubilalis(Hübner). The ground-dwelling spider community was best characterized as a hunting guild and consisted primarily of Lycosidae, Thomisidae, and Gnaphosidae. A gnaphosid species,Gnaphosa parvulaBanks, is a new state record for Iowa. Total ground spiders reached greatest numbers by June and declined thereafter. The foliage-dwelling spider community was characterized as both an orb-web guild and a hunting guild. Tetragnathidae, Araneidae, Salticidae, Thomisidae, and Oxyopidae accounted for 89% of the foliage-inhabiting spiders. Effects of carbaryl and fenvalerate applied for adult ECB control were tested on the spider fauna in action sites. Spider populations were generally not affected, except for the foliage spider family, Tetragnathidae, whose numbers were significantly reduced for 28 d in 1984 in treated action sites. It is suggested that beneficial spider populations, particularly ground-dwellers, could be protected from adverse effects of insecticide treatments if treatment was timed to miss peak densities and the application was primarily directed at the upper foliage canopy