These pages have often expounded the virtues of predator wasps and how to encourage them into the garden. But all wasps are not beneficial. European Wasp or Vespula germanica is an introduced pest from the northern hemisphere which is increasing its range in Australia. It makes its presence known at barbecues and al fresco eating places, menaces the dog and is attracted to some perfumes. It is a scavenger with a wide dietary intake which includes dead animals and sweet foods such as nectar and fruit.
It looks like a bee, with its black and yellow colouring, and is the same size as a bee.
Unlike the bee it can sting numerous times. One friend of mine was stung seven times by the same wasp on his inside thigh, as it made its way up inside his pants. He tells me it is a fierce sting, which takes from three days to a week to heal.
We have plenty of wasps in the Adelaide Hills and I find their nests in tree hollows, roof cavities and rubbish piles, excavated into clay banks or behind stone or sleeper retaining walls.
They are social wasps and like bees they have a queen and workers in large colonies, with the same life stages as a bee. I observe the queens flying or crawling over the stone walls of my house looking for crevices or gaps in which to start a new nest.
Even a small nest can be several thousand insects - about the size of a basket ball, larger ones can be half a metre across. The nest is made from wood, bark or other vegetation which the wasps chew to make a papery pulp and form into cells reminiscent of a bee-hive. If they run out of room in the wall or roof cavity of your house they will chew through gyprock to expand the nest. They prefer well drained and protected areas but will also build nests in very exposed areas, although many of these nests will be destroyed by cold or wet winter conditions and the colony will not survive.
Recently someone showed me over a site on which I was going to build a compost heap, for teaching purposes. When I had left, they attempted to clean up the area with a front end loader, uncovering a nest. I arrived several days later and began to chase the runners on some kikuyu which was left in the ground, plunging my garden fork straight into a nest. As I brought a portion of the nest to the surface a dozen angry wasps flew out. I dropped the fork and ran - fast. When I turned I expected to see the air thick with wasps, but only about a dozen or so were left. The nest had been treated, but no-one had told me. I was lucky I had not arrived a day before.
This result is unusual. Generally the pesticide used to destroy the nest does its job quickly. All wasps are usually dead within two to four hours. The loader bucket had open the back of the nest and some wasps were exiting through the new breach, avoiding the pesticide which had been pumped through the main opening.
Until recently Local Government has coordinated nest destruction, although an amendment to the local Government Act in July now requires South Australian landowners to be responsible for removing nests on their own land. The problem is becoming too big. More then 1500 nests were destroyed in the Stirling District (now amalgamated into the Adelaide Hills Council) last year, compared with 91 in 1992.
How did this unpleasant pest reach Australia? Probably through queens establishing a nest in pallets or other materials on a European wharf and arriving in cargo, by sea. Whatever the pathway, they are present, expanding their territory and there is slim chance that they will ever be eradicated.
Biological controls were investigated about fifteen years ago but nothing very promising emerged and although investigations into parasites and predators continues, most researchers are pessimistic. The wasps are fierce fighters so it is unlikely a predator will be found. So far the search for parasites and diseases has been unfruitful too.
Another wasp parasitic on Vespula germanica was released in Victoria but was not effective.
Professional baiting is reasonably effective at reducing numbers in a local area. This is usually done with a bait such as minced kangaroo meat and a poison such as Diazanon. The best control is to find the nest and apply the poison directly to it. various chemicals will be effective but a common and effective one is Coopex, which contains a synthetic pytrethroid in a carrier of talc.
I accompanied Trevor Dix from the Adelaide Hills Council on a nest destruction visit. We found the nest from instructions provided by the land holder, but it was not hard to locate. A steady stream of wasps was emerging from a nest in a rubbish heap and while they quickly dispersed once in the air, the activity at the nest entrance was obvious. Trevor wore gloves, a hat and face mask, but by moving slowly and quietly he was able to avoid alarming the nest. A bellows applicator with a long nozzle was used to deliver two puffs of the toxic dust and the first few wasps emerged seconds later. They had been strongly effected by the poison and were involved in a last intense and rapid flight before they dropped out of the sky. Most wasps would have been killed within minutes, inside the nest.
The nest may remain active for several hours because adults will be returning from foraging expeditions.
Approaching the nest without adequate protection and a ready escape route would be foolhardy. The wasps release an aggression pheromone when disturbed, so any other wasp within range will become aggressive and each one may sting many times. several Adelaide residents were attracted this year and received around fifty stings, requiring medical treatment.
The effect of the pheromone has be witnessed by the occasional Aussie, enjoying a warm day on the veranda, and casually swatting a few European wasps. Suddenly the wasps become aggressive, driven by the scent released from the squashed carcasses of their kin, and they attack, with a painful consequence.
Many residents try to bait or trap individual wasps. A typical trap is made from a ten litre bucket three quarters filled with water and hung in a tree. A piece of oxtail or other suitable bait is hung from the handle and dangles over the water. Perhaps some gauze can be placed around the handle, to restrict the opening. When the engorged wasps stop feeding and depart they drop down, and many will be drowned in the water (a little detergent in the water helps to overwhelm them).
This technique may be effective at reducing numbers in a very small area. If a number of neighbours all bait, the vigour of a nest could be seriously reduced, because it will reduce the total amount of foraging. It is unlikely that home made baits will kill an entire colony because of the number of individuals at any time and the rapid replacement rate of workers. There are so many wasps in the nest that many may simply never encounter a few baits within the hunting range. Baiting may lift the pressure of wasp numbers sufficiently to allow you to enjoy a BBQ again, but locating the nest and destroying it is the best method.
In bushland areas the nests can be very hard to locate. Many of the creeks in the Mount Lofty Ranges are overgrown with blackberry, an ideal cover for the nests. In these bushland areas the wasps are very effective at competing for every manner of food including carrion or sweet food such as nectar and rotting fruit. They will therefore displace native insects and animals.
The economic consequences of the wasp have begun to be felt in production horticulture and viticulture too. The effect of wasps on harvesting of crops is becoming a concern to some growers and a few vineyards in the Adelaide region claimed that up to fifteen percent of grapes were left on the vines this year. Apple producers are concerned that pickers will be hard to find in areas where the wasp is established.
While these pages seldom recommend the use of a synthetic pesticide, the placement of the pyrethroid into the nest itself is one of the few instances where the pesticide can be directed at the target, rather than at the ecosystem (in the hope of encountering the pest). Because of the environmental harm and economic damage which this pest can cause, and the small amount of pesticide applied, this form of nest is the safest and most appropriate until a biological or genetic control can be found.