Traffic rate as an index of colony size in Vespula wasps

The number of Vespula wasp workers in a colony can be predicted from the mean of 1-minute counts of wasps entering or leaving the colony (traffic rate). The predictive equation (Adjusted R 2 = 0.87) is: number of workers = 32.243 × traffic rate per minute and is independent of species, time of year, or location. However, we mainly measured mature colonies. The equation may overestimate the number of workers in spring colonies, because a greater proportion of workers forage then. Traffic rate can also predict the biomass of a V. vulgaris colony (Adjusted R 2 = 0.90) by allowing for season. Colonies measured after mid May generally had a larger biomass for any given traffic rate than those measured earlier. There were too few data from V. germanica colonies to evaluate the relationship between traffic rate and biomass for this species.