Herbicides are applied to commercial crops with increasing frequency and diversity yet are rarely tested for acute or chronic toxicity effects on beneficial non target species such as spiders We measured the lethal effects of chronic exposure to field relevant doses of herbicide treated soil on an agriculturally abundant wolf spider, Pardosa milvina. We tested six herbicides including atrazine, S-metolachlor, mesotrione, glyphosate, 2,4-D, and dicamba. We also tested a mixture of all six herbicides and a distilled water control. Spiders were housed individually in containers with topsoil previously sprayed with a recommended herbicide dosage or water control group To test for herbicide residue effects, we reared spiders under herbicides exposed to three aging treatments freshly applied herbicides, herbicides aged for 69 days under room temperature laboratory conditions (indoor aged) or aged for 69 days in a greenhouse with variable temperature, humidity, light exposure, and evaporative cycling (outdoor aged) (N=960; n= 40 spiders across 24 treatments) Spiders were maintained on these treated substrates for 48 days and fed crickets (Gryllodes sigillatus). We recorded daily mortality across all spider treatments during the testing period Mesotrione and combined herbicide treated spiders showed very high mortality within two weeks of exposure among both freshly applied and indoor aged soil treatments while mortality was modest across outdoor aged herbicide treatments. Our results indicate that some herbicides are arachnicides but require chronic and prolonged exposure to produce lethal effects. Further, soil bacterial communities alone were insufficient to break down herbicides or reduce their toxicity while photodegradation, bacterial action, temperature variation and evaporation cycles were sufficient to dramatically reduce toxicity during chronic exposure
