Wasps and Hornets

Risk/damage

Wasps, and particularly the social wasp, are mainly known for their nuisance value, particularly in the autumn. The combination of the cooler weather and a diet of fermenting fruit juices will make them irritable and, therefore, more likely to sting. Wasps, unlike a bee, will sting many times when aroused. Reactions will differ from person to person.

In public health terms the effect of the occasional sting is usually minimal and falls into the category of 'nuisance'. However, some individuals show a serious reaction to stings in the form of anaphylactic shock, which can lead to death. Additionally, stings in the mouths or throat can cause serious respiratory difficulties and on rare occasions death.

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Biology and behaviour

There are several species of social wasp found in this country, but all are similar in appearance. They are all bright yellow and black, about 10-20mm in length, except for the hornet, which is somewhat larger and brown and yellow in colour. Some bees are often confused with wasps but wasps have a very slim waist and are a lot less hairy than bees. Unlike honeybees, wasps do not swarm.

Wasps are beneficial garden insects, collecting insects and larvea etc. to feed to developing wasp larvea in the nest during the summer months. Worker wasps will feed on a variety of foods including fruits such as apples, pears and plums. They collect wood to construct nests and may damage the wooden fences and garden furniture in the process.

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Life cycle

The only wasps that can survive the winter are the young fertilised queens. A queen will emerge from her winter hibernation around mid-April, and find a suitable site for her new nest. In nature, this will be on a branch or inside a hollow tree, or underground.  Unfortunately, a loft space, wall cavity or shed will do just as well. They will not use an old nest, but may build on the side of an old nest. The queen then builds the first cell to the new nest herself using chewed wood pulp, known as wasp paper, and lays between 10 and 20 eggs. She feeds the resulting larvae until they emerge as workers, who then take over the tasks of enlarging the nest and providing food for the subsequent larvae, which mainly consists of other insects. The adults satisfy their craving for sweet foods by drinking a sugary secretion produced by the larvae.

The new nest will start the size of a golf ball and grow to full size by September. The nest will usually grow to the size of a football and will be home to about 5,000 individuals, but in some cases can be quite a bit larger. In the late summer a generation of males and young queens emerge. They mate and the queens seek a place to hibernate. The rest of the colony gradually die off as the weather cools, and the cycle starts again the next spring.

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Control

Individual wasps that enter a house or other property can be dealt with by using an ordinary fly insect spray. It is also advisable to avoid leaving sweet sticky foods around which could attract wasps to them. However, killing individual wasps will have no effect on the population; the nest would need to be found and treated.

If a nest is in a place where it gives a cause for concern there are a number of proprietary products available to kill the nest. Whichever product you use, you are advised to read the label and follow the instructions carefully, taking all necessary precautions. However, nests located away from human contact can be left untreated; wasps have a beneficial aspect as they kill many garden pests.

When treating a nest you should consider the risk of being stung. Whilst for most people this is a painful annoyance, there is a significant minority who are allergic to the stings, and can suffer very extreme reactions. Furthermore, if the nest is in a place where a ladder is necessary to gain access to it, you should take extra care.

It is probably better to delay any treatment until the cooler part of the day, preferably about dusk, as it is most likely that all the adults will have returned to the nest and will be much less active. Even without treatment a nest can only last one season.

You should consider using a professional pest control contractor if access to the wasp nest is difficult or if there is a high likelihood of being stung.

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