A great place for wasps

New Zealand has some of the highest densities of wasps in the world thanks to mild winters, no natural predators and abundant food. There are several species of native wasp, which are not a problem, but accidently introduced social wasps have become a major nuisance, especially in the southern beech forests.

Social wasps live in colonies producing honeycomb-like cells, have a complex social structure, and all participate in the raising of the young.

Two species of paper wasps are present here — the black and yellow Asian paper wasp, introduced in 1979, and the reddish brown Australian paper wasp, introduced in 1880s. The Asian wasp is found throughout the North Island and the top of the South Island, while the Australian wasp is only in the north of the North Island. Paper wasp nests are apple-sized, made from regurgitated woody material. Cells are exposed to the open air and male and female wasps are present. Paper wasps are slender and dangly legs are seen when airborne.

The common and the German wasps build much bigger nests (soccer ball size, but have been up to 1.7 x 3.75 metres) and are much more of a problem. Both are yellow and black, and appear very similar with only subtle differences in facial markings distinguishing them.

The German wasp, here since the 1940s, has a grey nest, while that of the now widespread common wasp, introduced in more recent times, is brown.

These wasps have become a real problem because of their ability to reproduce so quickly and because of what they eat. Recent work has shown them to be eating between 1.4 and 8.1kg of invertebrates per hectare per season. Not only are they eating native insects, but also newly-hatched birds and massive amounts of honeydew, produced by a native scale insect that sucks sap and excretes a sweet, sticky liquid. Many native birds, bats, insects and lizards feed rely upon this honeydew.

In beech forests especially wasp nest densities of 12/ha (or 10,000 worker wasps/ha) mean many native species are struggling to compete. The newer common wasp has been found to eat honeydew faster, and is displacing the German wasp in these forests.

Dealing with wasps involves locating and destroying the nest. This can be a challenge. Wasps generally fly less than 200m to a food source, so nests are within that zone. Nests are best detected at dawn or dusk on a sunny day, when the angle of sunlight is low and the wasps can be seen entering or leaving. Using a bait of catfood sprinkled with flour apparently helps to see them.

Once found, an insecticide powder is placed at the nest entrance — best done at night. The workers spread the powder within the nest, and it should be dead within 24 hours.

Permethrin is now used, as Carbaryl has become unavailable. Recent success with Frontline as a bait away from the nest looks a more practical option.

To be continued.