Herbicide treatments were used in glyphosate-resistant field corn, Zea mays L., to produce treatments with weeds growing for varying periods of time in a replicated field trial conducted in three different fields over 3 yr. Increased weediness increased the activity-density of Harpalus pensylvanicus (DeGeer) (Coleoptera: Carabidae), the most common carabid species collected in pitfall traps. Field crickets, Gryllus spp. (Orthoptera: Gryllidae), showed a similar response, with generally higher numbers caught in weedier plots. Other ground-dwelling arthropod species showed variable responses to weediness. Wolf spiders (Lycosidae) showed an apparent response to fresh organic matter and dead weed thatch after herbicide treatments in 2002. Although several arthropods common in the field plots ate second instar western corn rootworms, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), when the rootworms were presented to them on filter paper in the laboratory, rootworms were not consumed when presented to potential predators under a thin layer of soil. Predation on exposed larvae placed in the field for 24 h did not differ by treatment, possibly because the major species that differed by treatment were primarily herbivorous or omnivorous. Corn yields were lower in the weedy check plots all 3 yr, but no significant reduction in yield occurred in treatments with weeds present for 21, 31, or 41 d after planting, or in plots treated with preemergence herbicide only.