General

Three species of introduced social wasps are present in Canterbury, although only two of these, the German wasp (Vespula germanica) and the common wasp (Vespula vulgaris) are established.  The German wasp has been established since 1954 in the Region, but the common wasp is a more recent arrival and it now appears to be the dominant species in the Region. The common wasp has displaced the German wasp from beech forests containing honeydew although the two species appear to co-exist elsewhere. 

When the common wasp was spreading into the Region in the late 1980s and early 1990s very high densities of the species were recorded, but since that time populations have fluctuated at lower levels. Wasps however still occur at high levels particularly in beech forest where honeydew is readily available, and the number of nests can range between 10 and 36 per hectare depending on the season in beech forest. Their numbers are typically lower in pasture, scrub, hardwood forests, and in beech forests in areas where the rainfall is high enough to wash the honeydew off the trees.  Wasps feed on carbohydrates such as nectar, honeydew, ripe fruit juice, and honey from beehives to meet energy requirements. Protein sources are required to feed developing larvae and include live invertebrates and flesh scavenged from dead animals.

Adverse effects of wasps

Wasps have a major impact on indigenous ecosystems through competition for food sources and predation on native insects. In native forest, up to 90 per cent of the honeydew standing crop may be reduced in the peak wasp season, affecting the feeding of kaka, bellbird, tui, and silvereye.  The prey intake of wasps in northern South Island beech forest is estimated to be similar to that of the entire insectivorous bird fauna. The impact of this predation is both on the native invertebrate biodiversity and the native insectivorous birds with which wasps have 80-100 per cent of their identified diet in common. 

As well as having effects on biodiversity, wasps also have an effect on human activities.  Wasps affect public health through the use of their sting producing localised swelling and itching in most people, but are capable of causing a systemic hypersensitivity reaction in 3.3 % of the population. This swelling can range from large local swelling to swelling of the airways and anaphylaxis. Deaths from wasp stings are rare – approximately two people die every three years from wasp or bee stings. Medical attention is more common but it is not possible to attribute a specific number of hospitalisations or general practitioner visits to wasp stings. Wasps may also pose a public health hazard through transmission of disease organisms, although again this is rare.  Wasps are a significant source of damage to amenity values. Department of Conservation offices in Hanmer Springs, Mt Thomas, and Arthur’s Pass (Craigieburn and Mt White areas) all report disruption of recreational users of conservation areas by wasps. Landcare Research at Lincoln receives over 1700 calls annually regarding wasp nests in and around Christchurch.

The impact of wasps on economic wellbeing arises through their impacts on the beekeeping industry. Wasps compete with honeybees for food sources, and rob hives and honey processing facilities. In beech forest, wasps have reduced honeydew abundance to the extent that bees do not feed on it for three to four months of the year. There are potentially some losses associated with fruit production, although these are more likely from disruption than direct damage. Other economic impacts may include the occasional stock death, possible deterrence of possum feeding at bait stations, and the impact on the tourism industry of high wasp numbers at scenic locations.

Environment Canterbury's role

Wasp control is primarily the responsibility of the land owner/occupier.  There are no enforceable rules around the requirement to control wasps. 

Environment Canterbury can facilitate and assist community and land occupier selfhelp programmes to destroy wasps particularly if adjacent to areas of high environmental value to complement control operations, or in other areas if there is community support for control operations.  This would be done through the 'Biodiversity Pest Programme'.