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.

Wasps: Close encounter of a painful kind

The common and the large paper wasps are the most familiar wasps in the Maltese islands. 

Although a relatively small number of persons have ever been stung by one of these insects practically everybody is aware of this insect’s ability to defend itself by inflicting a painful sting. 

The yellow and black stripes are a form of warning colouration which informs potential predators that trying to eat a wasp will result in pain.

Both of these species are very common in the Maltese islands and can be found practically in every corner of the countryside sometimes very close to human habitats. 

They build a distinctive nest made of a paper-like material which they produce by chewing wood particles and mixing them with saliva to produce a thick fluid which dries on exposure to air. 

The nests are anchored to a vertical solid object such as a wall, rock face or tree trunk by means of a stalk. After building the nest they secrete an ant repelling chemical which they spread around the base of the stalk to prevent them from stealing the eggs or brood from the nest.

The nests of the two species look very similar and are built in similar places. 

The large paper wasp is slightly larger than the common paper wasp and builds a larger nest hence their Maltese names: żunżan tax-xehda (common paper wasp) and żunżan tax-xehda kbira (large paper wasp).

Paper wasps are predators. They hunt other insects which are then carried to the nest to provide food for the larvae. 

Wasps and are very important biological pest control agents and should not be destroyed.

Paper wasps are usually not very aggressive and will attack only if they or their nests are threatened. 

I have taken many close-up pictures of their nests and I have never been stung. The only trick is to move slowly away if they start behaving nervously and appear agitated. 

This article was published in The Times on 9.11.11

A true predator kills and eats another organism

In ecological terms predation is described as the interaction whereby one organism feeds on its prey. Predators may or may not kill their prey before eating them but the end result is beneficial to the predator and harmful to the prey. This has led to selective pressures on one another which have lead to an evolutionary arms race between the predator and prey resulting in various anti-predator adaptations.

Predators are usually classified by the way they feed and the way they interact with their prey. A true predator is one which kills and eat anther organism. It may hunt actively for its prey or sit and wait for it to approach within striking distance. Some predators such as the lion kill larger prey which they dismember and chew while others like dolphins eat their prey whole. Some predators like snakes poison their prey to subdue it or kill it before eating it.

Prey species have evolved several ways to avoid being preyed upon. One common form of defence is aggression. The electric eel uses an electric current to kill prey and to defend itself from other predators. Others animals use their tusks, horns and hoofs to defend themselves.

An interesting form of defence, common in birds, is mobbing. This is when animals attack and harass a predator to drive it away. This can be seen in many species of birds such as gulls which attach predator, including men, when these get anywhere near their nests.

Some animals are camouflaged to avoid being seen while others are brightly coloured and do not bother to hide themselves. Their colouration is recognised and remembered by predators as a danger signal and are left alone. These animals such as the ladybirds, wasps and the caterpillars of the spurge hawkmoths, are usually poisonous or bad tasting.

The humped crab spider is an aggressive predator that lives on flowers with which it easily blends. It prefers the large yellow flowers of the crown daisy, which are now in flower. It lies motionless in wait for an insect to land on the flower and then catches it with its forelegs. It bites it to inject a poison and holds on to it until it is paralysed or dead before it starts to suck its body. 

This article was published in The Times on 20.01.2010