Impact on invertebrates
The predation rate of wasps on some invertebrate prey species is also so high that the probability of them surviving is close to zero (Toft & Rees 1998; Beggs & Rees 1999).
Wasps consume between 1.4 and 8.1 kg of invertebrates per hectare each season, depending on the density of wasps. German wasps carry heavier loads (5 mg) than common wasps (2 mg).
In honeydew beech forest, of the identifiable prey items, about 27% were spiders, 23% caterpillars, 18% ants and bees, 16% flies, and 16% other.
The composition of prey orders in the diet of wasps varies with season and between years, suggesting that the availability of different prey species affected the diet of wasps. It is possible that wasps switch to other prey species when the abundance of a prey species becomes low. This means some prey species may be kept at low density by wasps, but not eradicated.
Modelling suggests that to conserve vulnerable species wasp abundance needs to be reduced by about 80 to 90%. Not all species will be equally vulnerable to wasp predation, so these estimates provide a maximum level of control required to conserve some species. Achieving a lower level of control is likely to be beneficial to less vulnerable species.