Impact on Invertebrates
The predation rate of wasps on some invertebrate prey species is so high that the probability of an individual surviving through the wasp season is virtually nil. Hence wasps probably reduce or eradicate populations of some invertebrates. Wasp abundance needs to be reduced by 80-90% to conserve some native invertebrate species.
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| See video of wasp attacking an orb web spider (bandits 4) | |
Very high wasp predation rates have been recorded for some invertebrate species. For instance, the probability of free-living caterpillars, which occur at the peak of the wasp season, surviving to adults was only 10-78 to 10-40, and the probability of an orb-web spider surviving to the end of the wasp season was 10-18. Through modelling prey survival as a function of wasp density it has been calculated 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. While it is likely that wasps limit the abundance of some invertebrate prey species, the degree to which they reduce prey density it is not known.
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.
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In honeydew beech forest, of the identifiable prey items, about 30% were spiders, 20% caterpillars, 20% ants (winged reproductives) and bees, 15% flies, and 15% other. |
Wasps consume between 1.4 and 8.1 kg of invertebrates per hectare each season in the western and northern South Island respectively, depending on the density of wasps. German wasps carry heavier loads (5 mg) than common wasps (2 mg).
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Wasp numbers |
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Impact on birds |