An overview of commonly encountered wasp species with information for safe treatment and removal of nests.
Wasp nest treatment and removal is amongst the more dangerous activities a pest manager undertakes. Although there are a number of common elements to wasp treatments no matter the species, there are certainly some specific considerations for some of the wasp species, especially for European wasps. Here we provide some tips on wasp nest identification, nest treatment and removal.
Australian paper wasp nests
Only a few species of Australian paper wasp cause issues around buildings. Identification is fairly straightforward as even without seeing a wasp, the nests have distinctive shapes that should allow accurate identification, especially when the location in Australia is considered.
Polistes humilis, which is actually called the Australian paper wasp, is found across Australia, and also in the North Island of New Zealand. The nests are located in sheltered areas, under eaves and the branches and large leaves of foliage (Figure 1). The nest has an open structure (the cells are clearly visible) with the nest hanging upside down off a single stalk. The nests are relatively small, only accommodating several hundred wasps at its maximum size. An unusual behaviour of Australian paper wasps is that they reuse old nests – sometimes a queen will overwinter, but sometimes new queens will start a new colony in an old nest.
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Polistes chinensis, the Asian paper wasp, is an invasive species, which is found in NSW and in the North Island of New Zealand and the top of the South Island. It is noteworthy in that it is often confused with the European wasp due to its black and yellow colouration. However, they have yellow antennae (European wasps have black antennae), and their nests and nest locations are similar to the Australian paper wasp.
Although less common, it’s important to mention a number of other native Australian paper wasps that belong to the Ropalidia genus. Ropalidia revolutionalis is found in Queensland. Their nests consist of thin combs only two cells wide, which are up to 10 cm long. They hang vertically in sheltered areas and often several nests will be hanging in a row (Figure 2). New nests are built each spring.
Ropalidia romandi, the yellow brown paper wasp, is found in Queensland and the Northern Territory. It encloses its nest in a paper shroud creating a ‘paper bag nest’ (Figure 3). Given the appearance of the nest and the appearance of the wasp itself (yellow with dark markings), it is sometime confused with the European wasp. However, it has a non-overlapping distribution (European wasps are not found in Queensland or the Northern Territory). They have some other similarities with the European wasp in that they can build large nests, they are very aggressive, and they overwinter; their nests can increase in size year on year. Interestingly they found new nests by swarming – a few queens leave the nest with a large number of workers.
European wasp nests
The term ‘European wasps’ actually covers two similar species, the German wasp (Vespula germanica) and the common wasp (Vespula vulgaris). Typically, they can be differentiated by looking at the heads, with the German wasp having three small black dots on the front of the head. Both species will build their nests either underground in raised banks (Figure 4) or above ground in sheltered areas next to objects. They are happy to build their nests on eaves and in roof voids. Both nests start with the queen building cells for the first brood.
However, as the nest increases in size, a shroud is built over the nest for protection and to maintain nest temperatures (Figure 5). However, there are also some notable differences in their nests. German wasp nests tend to be grey and are made from the fibres from sound wood whilst common wasp nests tend to be brown as they use fibres from dead or rotting wood. Typically, German wasps will produce slightly larger nests than common wasps and are more likely to overwinter, producing multi-season nests and extremely large colonies. However, identification is somewhat academic, as the treatment is the same.
Distribution of the two species within Australia is unclear. One or both species are present in NSW, generally not much further north than the Hunter Valley, throughout Victoria and Tasmania, and some areas of South Australia, particularly around Adelaide. Although the European wasp has been detected in Western Australia it is still listed as an exotic pest and is subject to an ongoing Government surveillance and treatment program to prevent it becoming established.
In New Zealand both the German and common wasps are well established. The prevalence of each species depends on the food available in each area. For example, common wasps, which are particularly efficient at collecting honeydew, dominate the beach forests in New Zealand where large amounts of honeydew are produced by scale insects.
Potter wasps and mud dauber wasps
Potter wasps and mud dauber wasps are solitary wasps that build small clusters of brood cells made of mud, in which they place paralysed prey and deposit an egg (Figure 6). The subsequent larva then has a plentiful supply of free food. The different species construct nests in different styles. They will be built in sheltered areas – under eaves, in the subfloor or in the garage are preferred locations.
Wasp nest treatment
Treating wasp nests in the evening is generally the best idea as the wasps will be back at the nest and generally calmer, as they are settling in to rest for the night. If the nest is in a roof void, where light is required to view the nest, the use of a red filter over any torch is advised (insects cannot see red light). Make sure suitable protective gear is worn – full protective gear with bee hood and taped joins in clothing is advised for European wasp treatments.
Australian paper wasp nests (and Asian paper wasp nests) can be easily treated with a direct spray treatment, either with normal spray equipment or a specialist wasp aerosol. Applying a treatment whilst standing on a ladder is not a safe practice. Use suitable equipment or a product that can be sprayed/applied from the recommended distance. Once the nest has been destroyed, it should be knocked down and removed.
European wasps and the paper bag nests of Ropalidia romandi should be treated using similar techniques and with a similar high regard for personal safety. For aboveground nests, the paper shroud around the colony prevents liquid insecticides being directly applied to the nest inside. Spraying liquid through the entrance hole is possible but requires a good deal of accuracy. With nests often being of a significant size, ensuring complete coverage of the combs for a quick kill is a challenge. Blowing powder through the nest entrance also requires accuracy but the powder is more completely circulated through the nest. The use of flexible conduit can allow the powder to be blown into the nest from a distance. For European wasp nests underground, insecticide dust should be blown through the nest entrance to fill the void.
Wasp traps have limited use, in that they will kill foragers but will not kill the nest. Wasp baits are an ideal option for European wasp nests, especially if the nest cannot be reached or located (e.g. on a neighbouring property). Foraging wasps will take the bait back to the nest, providing colony control.
Where possible, after treatment the wasp nests should be removed. Certainly, the customer doesn’t want an unsightly nest(s) remaining in place. For potter wasps and mud dauber wasps, it is best to physically remove and destroy the nest. Spraying the nest whilst still in place will leave streaky mud marks; better to physically remove the nest and then apply a residual treatment to the clean surface to prevent nests being rebuilt. Such residual surface treatments, as part of a general pest treatment, can be very effective in preventing wasps from building their nests under eaves for many months.
More information on pest control of wasps and general wasp information.
