Sunday, March 10, 2013

Wasps - Predatory flying insects

Wasps are predatory flying insects with two pairs of transparent wings and an ovipositor, which is a tube for laying eggs, which can be modified in various ways. 

In several species the ovipositor is used to sting and inject venom.  Most stinging wasps are predators or scavengers; their ovipositors may be modified to inject venom used for killing prey or for defence. 

In some species one sex may be wingless. In the vegetarian sawflies, the abdomen is broadly attached to the thorax and the ovipositor is rigid; in the higher wasps, the abdomen is flexibly attached to the thorax and the ovipositor is movable. 

The larvae of parasitic wasps consume the bodies of other insects or, in a few cases, consume plant tissue.

Wasps are related to ants and bees but separated from them by having a sting and no hair (bees have hair). Wasps prey on a large variety of insects and it is claimed that every pest species has a wasp species that preys on it making wasps important agents of biological control and they are often used to control agricultural pests.

About 75,000 species of wasps are known, most of them parasitic. Wasps are categorised into two main groups, solitary wasps and social wasps. Adult solitary wasps generally live and operate alone and most do not build nests. Social wasps live in colonies that can have several thousand individuals but in some cases not all members of the colony can reproduce.  In the more advanced species only the wasp queen and male wasps can mate, while the majority of the colony is made up of sterile female workers.

Many species of wasps build nests which could be a simple structure made of mud as is built by some predatory solitary wasps to large complex structures built by social wasps. Wasps do not have wax producing glands like bees instead they create a paper-like substance using wood pulp which is collected from weathered plant material which is softened by chewing and mixing with saliva. The pulp is then used to make combs with cells for brood rearing.

Several species of wasps can be found in the Maltese countryside. The most common are the paper wasps which build colonial nests which are fixed to sunny rock faces, walls and trees and wood. A colony consists of three casts, queen, female workers and males. Males do not have a sting. The two most common species are the common paper wasp (żunżana tax-xehda) and the large paper wasp (żunżana tax-xehda kbira). These two species are very similar and difficult to tell apart. 

This article was published in The Times on 2 September 2009.

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