There are over 2,000 different species of wasp in NZ and most of them are solitary wasps, i.e. they do not make nests. The five species that are a nuisance to us humans are all introduced and give the others a bad name.
If you are encouraging butterflies then you will be well aware of the main predatory wasps, the social wasps. Three of these species make paper-like nests hence the name 'paper wasp'.
At the beginning of the summer, social wasps are intent on nest-building, then laying eggs. When the eggs hatch the adults search for protein to feed their young..
Bingo! Caterpillars are a great source of protein. For several months social wasps will steal your eggs and caterpillars of all stages, even pupae. By the end of the summer the juvenile wasps will be adults, and then the wasps will all be seeking out nectar for energy (no longer protein for building better bodies).
Nests
Nest of Asian (paper) wasp, thanks Alison Meier
Paper wasps (Polistes spp.) build nests from chewed up wood material, hence their name. When flying, a paper wasp's long legs hang down below its body. Vespula species' nests are usually found in caves, trees and underground.
These wasps affect beekeeping operations as well as our native flora and fauna, and their stings can genuinely be a health risk. Be vigilant when outdoors around your property, looking for nests. Often they are in trees, bushes, or on buildings such as fences and the outdoor faces of homes and garages.
Controls
Tell the neighbours, pointing out what a pest these wasps are. Social wasps usually only forage within 200-300 metres of their nest. If you've located a nest, go out at dusk when the wasps are inactive and spray it or remove it with a plastic bag, tieing it off and putting it straight into the freezer. After 24 hours the wasps will be dead and you can put it into your rubbish.
"Wasp traps" may not be effective. So far we haven't found one that works (traps or baits).
Net curtains no longer useful for the house can be reused in the garden making it harder for wasps to "get into" your plants to attack the caterpillars. A mosquito net over a frame can also be used. Throw the net over your swan plant in the garden. Monarch butterflies have been known to lay eggs on the outside of the net and the caterpillars that emerge climb through the mesh onto the plant.
For monarchs, grow swan plants now for next year and encourage them to bush out by pinching out the new growth. Not only does it mean the plants provide more shelter and protection but also more food for more caterpillars. Plant plants close to bushes and shrubs that offer nectar (such as Hebes, or annuals like zinnias and cosmos) to give more shelter as well.
Please feel free to add more tips in the comments below!
Jacqui Knight this info is great... Best I've found is to catch the wasp in a net from $2 and sprinkle it with derris dust then let it free... It will be MAD however it takes the dust back to its nest and the others help to clean it off electively killing them.