Genetically modified organisms (GMO) in non-European countries are introduced into the agro-environment on large scale with little knowledge of adverse effects on biodiversity. In the European Union (EU) possible effects of GMOs on biodiversity have to be accurately and precisely monitored. Monitoring biodiversity with a high precision is expensive and may only be achieved in close cooperation between GMO monitoring and general biodiversity monitoring. The EuMon project sampled metadata on biodiversity monitoring in Europe. Basing on the metadata, we estimated resource needs for biodiversity monitoring as needed for detecting potential adverse effects of GMOs on biodiversity. On average the analyzed schemes with a potential to detect at least a 5% change of biodiversity monitor 242.6 ± 105.4 sites at 322.6 ± 172.1 person days employing 63 ± 23 persons per year. The time invested in monitoring, given as person days, however, differed greatly between schemes and species groups, so that real manpower might be considerably higher.