The sixth mass extinction event is underway and environmental pollution is one major driver. Of particular concern are global insect declines, as their roles in ecosystem functionality and human food security are indispensable. Even though environmental pollutants are known to reduce fertility, their potential effects on insect fitness remain poorly understood - especially for soil-dwelling species. Here, we show that fertility of soil-dwelling beetles, Aethina tumida, is reduced, on average, by half due to field-realistic neonicotinoid soil contaminations. In the laboratory, pupating beetles were exposed via soil to concentrations of the neonicotinoid thiamethoxam that reflect global pollution of agricultural and natural habitats. Emerged adult phenotypes and reproduction were measured, and even the lowest concentration reported from natural habitats reduced subsequent reproduction by 50%. The data are most likely a conservative estimate as the beetles were only exposed during pupation. Since the tested concentrations reflect ubiquitous global soil pollution, the data reveal a plausible mechanism for ongoing insect declines. An immediate reduction in environmental pollutants is urgently required if our aim is to mitigate the prevailing loss of species biodiversity.