Wasps (social) including hornets

Wasps are beneficial in gardens, they feed their grubs on caterpillars and other insects and can reduce pest populations. Wasps can be a nuisance mid to late summer and may damage ripe fruits. Disturbing a wasp nest when weeding or hedge trimming can result in multiple painful stings. 

Common wasps feeding on pear fruit

Common wasps feeding on pear fruit

Quick facts

Common name Wasps (social) and European hornet
Scientific name Vespula species, Dolichovespula species and Vespa crabro
Plants affected Ripe fruits, including grapes, pear, plum and apple
Main cause Social wasps
Timing May-October

What are social wasps?

'Wasps' can describe many species including the predatory solitary wasps and parasitoid wasps. Social wasps live in colonies and in Britain are usually yellow and reddish brown or black. 

Seven species of social wasps commonly occur in gardens in Britain. Vespula species of wasps, such as common wasp (V. vulgaris) red wasp (V. rufa) and German wasp (V. germanica) usually make their nests underground or in dark cavities, such as roof spaces. Dolichovespula species of wasps, such as the media wasp (D. media), Saxon wasp (D. saxonica) and tree wasp (D. sylvestris) usually make their nests in open air situations, such as on the outside of a building or among the branches of a tree or shrub.

The hornet (Vespa crabro) is Britain’s largest social wasp and it has become more common recently. Although its size can cause alarm it is much less aggressive than other species of wasp. It is a useful garden predator and will predate on other species of wasp. It nests in rot holes in trees and other dark cavities.

Another species of hornet, the Asian hornet (Vespa velutina) has become established in France and some other areas of mainland Europe. The It is smaller than the European hornet and has only one yellow stripe on its abdomen whereas the native hornet has several yellow stripes. More information including an identification guide can be found at the non native secretariat. Anyone who believes they have found an Asian hornet or nest should not go near it and report it to alertnonnative@ceh.ac.uk. The Asian hornet should not be confused with similar looking insects including the European hornet which can be a useful predator of other invertebrates including other social wasps.

In 2017 two nests of the Asian hornet were found in England and in 2018 four, all were destroyed. There have also been a number of sightings of individual Asian hornets. It established in the Channel Islands but eradication attempts in England are currently thought to be successful. 

Symptoms

The presence of a wasp nest can be recognised by a steady stream of yellow and black-striped (ginger in the case of European hornet) insects flying to or from the nest entrance. Adult worker social wasps are about 15mm long but smaller individuals can occur, particularly in late spring. Queen wasps are larger and are 20-25mm long. Hornet workers can reach 25mm long and queens 30mm. Wasps are more slender and less hairy than bumblebees, which may also nest in the ground. Honeybees and most solitary bees are also hairier than wasps. Although nomad bees can appear superficially similar to wasps.  There are also numerous species of solitary wasp in the UK, these solitary species can nest in close proximity to one another, but each female will have her own nest entrance. Solitary bees and wasps either have no sting or are very unlikely to sting. There are also many species of hoverfly that are wasp mimics.

Worker wasps feed the grubs in the nest on other invertebrates such as caterpillars and aphids. This activity can reduce pest problems in gardens in early summer. Later in the summer when wasp nests have passed their peak the demand for animal protein in the nest is lessened and wasps often to seek sugary substances.

Damage to plants is limited and mainly occurs in late summer, when social wasps can feed on ripe fruit. On tough-skinned fruits, such as apple, wasps enlarge cavities that have been initiated by other animals, such as bird pecks. On fruits with softer skins, such as grapes, plums and pear, wasps can initiate the damage.

Wasps can present a hazard if a wasp nest is disturbed. For example this can happen when compost bins are being emptied, hedges trimmed, rough grass is being mown or when flower beds are being weeded. Wasps will defend their nest by stinging anyone or animal who is nearby. If left alone wasps tend not to be aggressive. NHS Advice on stings  

Worker wasps that are building the nest structure will gnaw wood fibres from wooden garden furniture, sheds and fences. This causes paler patches where the surface has been scraped off but no real damage is done.

Control

Where possible wasp nests should be left alone, they can help control nuisance invertebrates. The nests die out in late summer or autumn. Although never re-used the papery constructions can last several years.

Non-pesticide control

Wasp damage on fruits can be reduced by enclosing some of the fruit trusses in bags made from muslin, nylon tights or similar fine meshed materials. Grapes in glasshouses can be protected by fixing a wasp-proof screen over the door and vents. Foraging wasps can be trapped in jam jars half-filled with water plus some jam. The top is covered with a sheet of paper held on with an elastic band. Punch a hole in the centre of the paper with a pencil to allow wasps to enter. They will be attracted by the scent of the fermenting liquid and will drown. A wide variety of wasp traps are also available from garden centres and hardware stores. Although it is not clear if these traps reduce wasp numbers locally or attract more wasps from further afield.

Pesticide control

There is a wide range of pesticides available for wasp control, label instructions must be followed. Some are dusts applied to the nest entrance others are foaming aerosols which can be applied some distance from the nest entrance. This should be done in the evening when fewer wasps are flying. There is always a risk of being stung when attempting wasp nest control. There are also pest control contractors who kill wasp nests.

Biology

In spring, queen wasps emerge from sheltered overwintering sites and seek suitable places where they can establish nests. Initially a queen wasp is on her own and does all the nest building and food gathering for the first brood of larvae. The initial queen nest is about the size of a golf ball and contains a small piece of comb with hexagonal-shaped cells in which the queen lays eggs. The larvae are white, legless maggots that  pupate in their cells. Most emerge as infertile females, known as worker wasps. Once workers are available they increasingly take over the tasks of building the nest and gathering food, allowing the queen to remain in the nest and lay eggs. By late summer, a wasp nest can be larger than a football and contain 400-500 worker wasps. At that time, males and fertile females are produced, with the latter becoming next year's queens. The nests of Dolichovespula species decline and die out in late summer but those of Vespula species and the hornet can continue into late autumn. The workers, males and the old queen die at the end of the season and only the young queens overwinter. They leave the nest and seek sheltered places elsewhere, such as in outbuildings or under loose bark

Wasps gather material to construct their nests by rasping wood fibres from fences, garden sheds and other suitable exposed wood. The fibres are mixed with the wasps' saliva to make a paste that can be moulded by the wasps' jaws to make the combs of hexagonal cells and the outer envelope that encloses the nest. Unlike bees, which feed their larvae with nectar and pollen, wasps are mainly predatory. The worker wasps capture other insects or feed on carrion. The food is chewed up by the worker wasps and partially digested before being regurgitated and fed to the larvae.


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