Wasps at the outdoor table in late summer

Early summer meals outside are mostly about the food. By late summer and autumn, they can be about the wasps. One arrives at the ham, then another lands on the rim of a glass, and suddenly everyone is waving their arms and the salad is going back inside.

There is a reason it gets worse as the season goes on, and a few simple habits make a real difference.

Why New Zealand has so many

The Department of Conservation’s wasp page explains that New Zealand has some of the highest densities of German and common wasps in the world, because they have no natural predators here, the winters are mild and there is plenty of food. Five social wasp species have been accidentally introduced since the 1940s and are classed as pests: German and common wasps, and three paper wasps.

German and common wasps are the familiar black-and-yellow ones that build large papery nests, often underground or in wall and roof cavities. Paper wasps are slimmer, with long dangling legs, and build small open nests under eaves and on fences.

Why they come to the table later in the season

Through the warmer months, wasp colonies grow fast and workers hunt protein, mostly other insects, to feed the developing young. DOC notes that this is when protein baits work. As the colony matures towards the end of the season, foragers increasingly scavenge. The University of California’s guide to social wasps describes the same pattern in its closely related yellowjackets: late in the season, foraging wasps turn up at picnics and barbecues, around rubbish bins, at pet food left outside and wherever ripe or overripe fruit is lying about.

So the meat on the barbecue, the sweet drinks, the fruit platter and the bin by the back door all look like dinner.

Keeping food and drinks covered

• Cover everything until it is served. Mesh food covers, upturned bowls or plates over dishes, cling film over salads.
• Cover drinks. Use cups with lids or straws, or check before every sip. The University of California guide specifically suggests covering soft drink cans so wasps do not crawl in. A clear glass is safer than a can, because you can see inside it.
• Serve in small amounts and bring dishes back inside as soon as people have finished.
• Clear up straight away. Scrape plates into a lidded bin, wipe sticky spills on the table, and do not leave the barbecue plate dirty.
• Keep bins sealed and empty them regularly, as both DOC and the University of California advise in their own ways. Rinse food scraps out of the recycling.
• Pick up windfall fruit under plum, apple, pear and feijoa trees. Fermenting fruit on the lawn is a wasp feeding station.
• Feed pets inside, or lift the bowl as soon as they finish.

Stay calm if a wasp lands on you or the food. Swatting tends to make things worse. Move slowly away, or let it leave on its own.

Where nests hide around a house

German and common wasp nests are often hidden, which is part of why they surprise people. Look for a steady stream of wasps flying in and out of one spot:

• a hole in the ground under a hedge, a bank, a compost heap or long grass,
• a gap in the weatherboards, soffit or roofline,
• a hollow in a fence post, a pile of timber or an old tree stump,
• the space under a deck or a garden shed.

DOC suggests searching on sunny days near dawn or dusk, when the low light shows up the flight path as wasps go in and out. Paper wasp nests are easier to spot: small grey combs hanging under eaves, on fences, in shrubs or on the underside of outdoor furniture.

Why not to take on a nest yourself

DOC gives instructions for treating a single accessible nest with insecticide powder after dark, and some people manage it. We would still leave most nests to a professional, especially around a family home, for these reasons:

• Nests are larger than they look. Much of a German or common wasp nest can be hidden in the ground or inside a wall.
• Disturbed wasps defend the nest in numbers. Stings are far more likely when the nest itself is disturbed.
• Nests in walls and roofs can be hard to reach, and treating the wrong spot just moves the problem.
• Ladders and wasps are a bad combination.
• Pesticides around food areas, children and pets need care that a contractor is set up for.

A licensed pest controller will find the nest, treat it properly and tell you when it is safe to use the area again.

Bee swarm or wasp problem?

In spring and early summer, people sometimes see a dense, buzzing cluster of insects hanging from a branch, a fence or a letterbox, and assume the worst. That is usually a honey bee swarm: a colony on the move, resting while scouts look for a new home. Swarming bees are generally calm, the cluster is brown and fuzzy rather than shiny black and yellow, and there is no papery nest.

Do not spray a swarm. Keep people and pets away, and contact a local beekeeper or beekeeping club for advice; in Auckland, Auckland Bee Help explains who collects swarms and when it is free. Swarms often move on by themselves.

A wasp problem, by contrast, is a steady stream of black-and-yellow wasps going in and out of a hole or a papery nest, day after day.

A calmer end-of-summer table

Covered food, clean plates, sealed bins and fruit off the lawn will not make wasps disappear, but they make your table much less interesting than your neighbour’s. And if there is a nest by the back door, the best thing to bring to the barbecue is a phone call to someone who deals with them for a living.