Background

1. Being stung by a wasp is painful. Wasps will sting their 'enemies' if they are being attacked or if their nest is disturbed. But wasps do have beneficial effect, being predatory on other insects such as flies and caterpillars that may be harmful. This paper aims to provide some advice to the public to avoid being stung by a wasp.

Insect Biology

2. Wasps belong to insect order Hymenoptera which is also shared by bees. Quite different from bees, which only sting once, wasps are stinging insects that are able to withdraw their stings for use again and again. A wasp has 'wasp-waist' caused by a deep constriction between the thorax and abdomen. They have two pairs of membranous wings and have yellow and black markings on their bodies.
3. They develop with complete metamorphosis: egg, larva, pupa and adult. The adult wasps are of three forms: male, female and worker. The males and females are reproductive with the females (or queens) founding the nests and laying eggs. The workers are sterile females. Each female and worker wasp is armed with a sting used for defence against predators. The male is unarmed.
4. A new nest is started by a single female (queen) in the spring. After several generations and under favourable conditions, new males and females are produced in the summer or autumn. The fertilized females then hibernate over the winter and become active in the spring. Males and workers die off in cold weather. Towards the end of autumn, a wasp nest reaches its maximum size. The nest usually lasts for one year.
5. Wasps are mainly carnivorous feeding mostly on other insects such as caterpillars but they also feed on nectar, tree sap and rotten/over-ripen fruits. They feed on liquids containing sugary materials too.

Distribution

6. Wasps may live solitarily in ground holes, clay pots, or bamboo stem cavities. Species that cause nuisance, however, are social insects and live in papery nests hanging from trees or building surfaces. The most commonly found species are:
   1. Vespa bicolor
   2. Vespa affinis
   3. Polistes olivaceous
7. They may fly 2-3 km to search for food. Large aggregation of wasps is usually caused by food attraction.

Public Health Importance

8. Most people stung will experience pain, swelling and itching at the sting site. The severity of reaction depends largely on each individual's response. For cases with severe allergic reactions, treatment by a qualified medical practitioner should be obtained as soon as possible.

Control Methods

9. Destruction of wasp nest requires professional knowledge. Pest control operators should be invited for carrying out wasp control work. However, appropriately labelled ready-to-use aerosol knockdown insecticides can be used against individual wasps.

Advice to the public

10. Some precautions to avoid being stung by wasps are:
    1. Do not disturb wasp and more importantly, wasp nest. Any disturbance may provoke stinging
    2. Do not leave food and drink uncovered, especially ripe fruit and soft drinks. Any scent of food especially sugary substances will attract many wasps
    3. Keep refuse in tightly sealed containers
    4. Avoid going barefoot in vegetation
    5. Avoid intruding wasp's territories
    6. Avoid using perfume or scented soaps, and avoid wearing brightly coloured or patterned clothing as they attract insects
    7. Avoid being stung on the head, mouth and throat by, for instance, pulling a portion of your clothes over your head
    8. Remain calm and move slowly away from wasp when being approached by it. Be sure that you can see where you are going. The insect will eventually leave of its own accord
    9. Seek medical treatment after being stung by wasp

Pest Control Advisory Section