Q What types of wasp might I come across?
A Wasps are a large family of mainly helpful insects, of which two species are painfully familiar to gardeners. The most frequently seen wasps are the common wasp (Vespula vulgaris) and the German wasp (Vespula germanica), two fairly similar types. The most abundant wasp in Scotland is the Norwegian wasp (Vespula norwegica). Hornets (Vespa crabro) are a large, uncommon and non-aggressive wasp species. There are also tree wasps (Dolichovespula sylvestris), red wasps (Vespula rufa) and the cuckoo wasp (Vespula austriaca). They all look distinctively wasp-like, so telling them apart is an expert job. Ordinary adults are female and 13mm long. Males and queen wasps are slightly larger.
Caption: Wasps feed on fruit that has been damaged by birds
Q What could I mistake them for?
A If you find a very large wasp with a long 'sting' (actually for egg laying) and no wasp waist, it’s a giant wood wasp (Urocerus gigas) female. They’re harmless. Hoverflies (Melanostoma species) can be brown or have yellow and black banding and are the same size as wasps. They mimic wasps and bees to avoid being eaten by predators. Hoverflies can occur in large numbers and can be recognised by their distinctive hovering and darting flight. Being flies, they have only one pair of wings. Some species are useful predators of garden pests, others scavenge dead material. None sting.
Q What damage do wasps do?
A Their stings are well known. Wasps also attack plums, grapes nectarines and late strawberries. The sweetest varieties seem to suffer most. Hard fruits, such as apples and pears, are only attacked if they have been damaged.
Occasionally wasps damage dahlias, rasping away the succulent stem and leaf-stalk tissue, apparently to get water. They can also be seen collecting wood for their nests from garden furniture, posts, fences, trellis and buildings, but do little real damage. They also rob beehives, but usually the bees can defend themselves.
Q When should I expect to see them?
A Wasps nests die at the end of the summer, with the queens dispersing and hiding in dry, sheltered spots. In spring, the surviving queens build new nests. Different species have different preferences for nest sites. The nest is built of chewed-up wood and saliva, which looks like paper. The queen builds it as a suspended ball, adding cells as her brood increases. Later, she stays in the nest and worker wasps do the foraging and building. The nest contains many cells, in each of which the queen lays an egg. This hatches into a grub, which becomes an adult after pupating. The adult wasps can become numerous by midsummer.
Young queens and males are produced and mate in late summer. Workers and males live until the cold weather sets in. A new colony starts from scratch each year.
Q Should I destroy their nests?
A If you can find the nests, destroying them will reduce the number of wasps locally, but nests are still likely to exist in neighbours' gardens and other places you cannot get at. To find nests, watch the lines followed by flying wasps on a still, warm day. They will converge on or diverge from nests.
Nests should only be destroyed with approved products. Sprinkle the dust around the entrance to the nest. Returning foragers will carry the dust into the nest, killing the queen and grubs. This is best done at dusk, as the wasps will defend their nest at other times. If necessary, tape an old spoon full of wasp killer to a cane in order to get it near the nest. This should prevent you from being stung and help you to reach awkward spots. When the nest is in too tricky a place, the local authority pest control officer may be able to help.
Q How do I keep wasps away from fruit?
A Insect-proof mesh over doors and ventilators will keep them out of greenhouses. Netting outdoor fruit to keep birds off will reduce the bird damage that encourages wasps.
Q Are wasps useful to gardeners?
A In spring and early summer wasps feed mainly on insects. Although they do sometimes feed on honey bees and other useful insects, on balance, they seem to consume mainly pests. In addition, the adults feed on the nectar of flowers, so they’re potential pollinators.
Q Should I control them?
A Since wasps are useful, it is best to spare them wherever you can. However, if they are especially numerous, cover food to avoid contamination, and don’t let children play close to a nest.
Q Should I kill single wasps?
A No. It’s only worth it indoors. Aerosol sprays will knock down the occasional wasp, but remember that a dead wasp can still sting, so be careful.
Q Will killing the queens keep the remaining wasps away?
A Because queens will move into gardens from outside, killing any queens you find won’t stop wasps invading your garden next year. Whatever you do in your garden is unlikely to have any lasting effect, as more wasps can arrive from up to one kilometre away.
Q What about wasp traps?
A Jars part-filled with diluted jam or other sweet liquid can lure in and drown wasps. It can help to get rid of annoying ones indoors, or distract them from a picnic, but where lots of fruit or jam is being prepared or especially delicious fruit is grown, you may find your traps don’t make much difference.
Q How do I protect my wooden structures?
A If wasps are doing significant damage to wooden structures, or furniture, apply a wood preservative. This is best applied during winter.