Nationwide survey of social wasps (Vespinae) in Finland

Global change affects species distribution and abundance. To monitor changes in the distribution and abundance of social wasps (Vespinae), reliable baseline data are needed. We established a network of study sites (n = 16) to study vespine abundance throughout Finland, ranging a 1 100 km south to north distance, during 2019–2024. Similar beer traps were used in all sites. Altogether 4 099 individuals and nine species were captured. The most abundant and frequent species was Vespula vulgaris (60% of individuals and 92% site-year occupancy) followed by Dolichovespula media (31% and 81%) and Vespa crabro (3% and 4%). Vespa crabro was only trapped in Åland Islands, but abundantly. Variation in the abundance of V. vulgaris and D. media was great among sites and years. Our study suggests great spatio-temporal variation and species-specificity in beer trap catches of social vespine wasps, which should be considered in designing monitoring protocols.