Native solitary hunting wasps
Compared to most countries, New Zealand has few native stinging wasp species – just 29, in two families. They can give a painful sting, but only under extreme provocation. All are solitary hunting wasps, not naturally aggressive to humans, being more intent on finding food for their offspring.
The 11 species in the Pompilidae family all prey on spiders, which they paralyse with venom and then drag into their 'nest' – usually a hole in the ground. Here they lay an egg on the paralysed spider, which becomes the only meal the wasp larva ever has, from the time it hatches until it is fully developed.
The golden hunter (Sphictostethus nitidus) hunts on the ground for the large brown vagrant spider (Uliodon species) and the tunnel-web spider, and in bushes for nursery-web spiders.
The large black hunter (Priocnemis monachus) prefers large, ground-dwelling spiders, including tunnel-webs and trapdoor spiders that make lidless burrows in the soil.
The 18 species of the Sphecidae family (the closest relatives to bees) prey on various insects and spiders. The commonly seen mason wasp (Pison spinolae) makes nest cells of mud, and stocks them with paralysed orb-web spiders.
Introduced stinging wasps
The most offensive stingers are four introduced species of social wasp in the Vespidae family. These are pests in urban, rural and natural ecosystems. The worst two are of European origin, the black-and-yellow German and common wasps (Vespula germanica and Vespula vulgaris respectively), which attack and sting to defend their huge nests. Both species, especially the common wasp, have invaded native forest – kauri forests in the north and beech forests in the south.
Effects on native ecosystems
These wasps eat vast numbers of native insects, in direct competition with insect-eating birds. They also feed heavily on beech forest honeydew, an important food for native insects and birds such as kākā and bellbirds. Their numbers are highest in late summer, and in some South Island beech forests their combined weight may exceed that of all the birds. They can make outdoor recreation unpleasant and hazardous.
Bee and wasp venoms are a complex mix of proteins, serotonin and histamine. It’s the histamine that causes pain and swelling. Medical help is usually only necessary for stings in the mouth and throat, and for hypersensitive and allergic people (0.5–2% of the population). Some may suffer anaphylactic shock and death. On average, two people die from wasp or bee stings every three years in New Zealand.
These wasps make papery nests from dry plant fibre mixed with their saliva. The two introduced paper wasp species prefer life in the open – in city and suburban gardens, farmland, scrub and open country. They make nests in shrubs and small trees, under the eaves of buildings, or even hanging from fencing wire. Their nests are small – a suspended ‘umbrella’ of paper cells. Towards the end of summer this reaches a maximum diameter of 7.5 centimetres, with about 200 cells.
The Australian paper wasp, Polistes humilis, a black and reddish-brown species with yellow markings and legs, arrived in the late 19th century.
The Asian paper wasp, Polistes chinensis, arrived in New Zealand more recently. It has the black-and-yellow pattern associated with wasps.
Both species are abundant in the northern North Island. The Asian species is still spreading south and may become established throughout New Zealand. Both are voracious predators of small insects, particularly caterpillars of various moths and butterflies. The Asian paper wasp captures monarch and copper butterfly caterpillars, and is blamed for the apparent decline in copper butterfly numbers.