There are four introduced wasp species in New Zealand: the Australian paper wasp; German Wasp; common wasp; and Asian paper wasp. Unfortunately there is also a fear that a big and potentially harmful new variety, the exotic yellow flower wasp, may have arrived in the far north.

Introduced wasp species are causing a number of problems through New Zealand as this country provides a favourable habitat, there are no natural predators, winters are relatively mild, and there is a plentiful food supply. They pose a danger to workers in industries such as viticulture and forestry, and they raid hives and diminish the food supply for honeybees, reducing their productivity. They also pose an environmental threat, consuming large numbers of native insects which are an important food source for many of our native species including kaka, tui and geckos. New Zealand has some of the highest densities of common and German wasps in the world - it has been estimated that the South Island's beech forests can be home to as many as 18 billion wasps in a season! However, wasp densities depend a lot on the spring weather and rain at nest-founding time has reduced the number of nests for the sixth consecutive season in some parts of the North Island.

An eradication programme for wasps is not feasible because wasps are highly mobile and there are few effective total control methods available. Taking a pro-active approach to wasp control will reduce the risk to yourself, your family members and neighbours, of stumbling over a nest and being attacked. The most successful way of reducing a local wasp population is to find and destroy all the nests. Wasps will most often search for food within 200 metres of their nest. If you can kill all the nests within the 200 metres of the trouble spot you should significantly reduce the wasp problem. Remember that wasp control is ongoing, the area may be re-invaded the following year.

Wasps build their nests in a variety of places: underground, often in sunny spots, along banks, attached to walls, plants and under the floor and eaves of houses. The best time to search for a nest is on a sunny day, preferably at dawn or dusk. This time of day is good because the low light highlights the wasps flight paths as they go in and out of their nests. You can track them in a number of ways. One of the more successful is to use a plate of cat food to attract them and, as they land, sprinkle them with flour to make them more visible. Follow the wasp as far as you can then repeat the process until you find the nest.

Powdered insecticides including Permex and Carbaryl are available for control. The dust is sprinkled liberally over and around the entrance of a nest after dark. The dust is carried into the nest by the wasps as they fly to and fro, effectively killing the wasps in the nest. The process may have to be repeated every seven days depending on the nest size. The smaller paper wasp nests (which are above ground) can usually be controlled using household fly spray. Chemicals for wasp control can be purchased from most garden centres and farm supply stores.

Petrol or diesel can be poured into a nest which is then plugged with a sack. This will fumigate the wasps, burt should be used sparingly. DO NOT set light to the nest. Small paper wasp nests that are hanging from a tree or branch above ground can be enclosed with a plastic bag and snipped from the tree. Place the bag and nest in the freezer for at least 3 days to kill the wasps, and dispose in the rubbish.

A wasp parasatoid Sphecophaga vesparum has been trialled by Landcare Research. The parasite hatches in spring, in time to invade wasp nests and destroy immature wasps. The parasites have established in two sites in New Zealand but have not reduced wasp numbers significantly. Microbial pathogens (such as fungi, bacteria and viruses) are currently under investigation by research teams from Landcare Research and AgResearch. The research may provide valuable results for control of wasps in the future.

REDUCE THE RISK: There is little you can do to avoid being stung by wasps as insect repellants do not work. Wasps are unlikely to chase after you unless you have disturbed a nest. When you are walking through bush in spring or summer time, particularly if you are in honey-dew beech country, be wary of where you put your feet and what you brush your pack on. Wear light coloured clothing. Wasps, as with honey bees, will direct their attacks against dark coloured objects (particularly blue) when disturbed.

KNOW YOUR WASP: An average wasp nest can produce between 1000 - 2000 queens per season. Queen wasps will fly up to 70 km in search of a nest site, however 99% of wasps fail to establish nests the following spring. Nearly all the worker wasps (the ones we see most often) die before they are three weeks old. A wasp sting in most people will cause a raised itchy painful swelling, but in a small proportion of the population will cause severe reactions, sometimes rendering people unconscious. About 10% of people are allergic to stings. You can be stung several times and think that you are okay, but the next sting may give your body a shock.

FIRST AID:Cold pads and antihistamine cream will help reduce pain and swelling. Seek medical advice immediately if there are multiple stings, or the victim shows symptoms of nausea or shock. If members of your party are allergic to wasp stings ensure they carry medication at all times and that there is somebody else capable of assisting them if need be.

(courtesy of Environment Waikato Regional Council, Animal Pest Series No 5 1998, and Alan Samson, Dominion reporter 20 Jan 2001)