Micscape Article: Wasp Warriors - The Wasp Sting.

by Maurice Smith.

Wasps - warriors of the air, and feared by all. What is it about these tiny creatures that causes even the bravest adult to run around the garden as though chased by a lion... the wasp sting!

Evolved mechanism
Wasps are predators. Along with ants, bees, and some other insects they belong to the order called Hymenoptera; sub-order - Apocrita. There are two sections within this sub-order: Parasitica and the Aculeata, with wasps belonging to the latter. The stinging mechanism has evolved from the ovipositor which, although used by many other insects for egg-laying, is now redundant for this function in the wasp. A good point to remember is that as the stinging mechanism actually evolved from the female egg-laying organ, it is only the females of wasps and bees which actually sting. (Small consolation though because you are most unlikely to meet a male of either these two insect groups).

Anyone who has seen the famous film called Aliens will have witnessed the Alien queen laying eggs from her giant ovipositor.

An ovipositor can be described simply as a complex sheathed tube designed for piercing the ground, plant tissue, or the bodies of other insects or animals, the egg being passed down the inside of the tube and into the host. With this in mind, it is easier to understand how the stinging mechanism has been formed by adaptation from this original organ.

Housing and protection
The wasp sting is housed in the abdomen (the rear of the insect). It consists of a poison sac attached to a set of components termed the lancets and stylus; a set of muscles also form part of the complete apparatus. Normally, no part of the mechanism is visible as it is protected within the abdomen casing. When the wasp goes to sting its victim, the two halves of the abdomen casing open slightly to allow projection of the lancets and stylet. In Fig 1 you can see the two sides of the abdomen A and B opening either side of the dashed line. The piercing components of the stinging apparatus are just emerging from the abdomen.

Whilst observing and filming this moment, the projected lancets were seen to sweep in an arc to and fro along the slit of the open abdomen. The direction and movement is indicated by the heavy black line C.

The fatal stab
The wasp does not really carry out a 'stabbing' action when stinging. Instead, the shaft is thrust into the victim and the lancets move rapidly backwards and forwards (sliding along the stylet) in a sawing action. The lancets are barbed - that is, they have small backward-pointed hooks along their edges. As the shaft penetrates further into the victim's body, the barbs allow anchorage against the flesh until the alternate lancet moves forward and 'claws' the shaft deeper into the wound. The movement of the lancets also enables a pumping action to take place at the abdomen end of the shaft. This causes the poison sac to pump venom down through a central poison canal, between the lancets and out through the shaft tip into the wound. The two lancets of the shaft are clearly visible in Fig. 2. Both Bees and Wasps sting their victims using a similar process but there is an essential difference, especially important when the victim being stung is a human-being. Bee lancets have larger barbs than wasps. The bee is unable to rip the shaft back out through the wound due to the barbs' resistance against the firmness of human flesh. The wasp stinging apparatus has lancets with very small barbs, more like fine serrated edges. A wasp can extract the shaft and fly happily off contented with having executed a nasty attack (or is it defence?) on the hapless human, whilst the poor old bee ends up having the entire stinging apparatus, poison sac and all, wrenched out of its abdomen. The bee will later die due to the damage caused.

Poison
The exact composition of wasp (and bee) venom is not known. It is a complicated chemical cocktail which contains enzymes and proteins as well as other things. It is rare for a healthy human adult to suffer death from a single wasp sting, although some individuals may be over-sensitive to the contents of the venom. In such cases, the victim may have an allergic-type reaction, go into shock, and may die as a consequence. Antihistamine solutions are used effectively in these cases and can reduce pain and discomfort and prevent death if used quickly enough. There is no known antidote to the wasp venom but, apart from a painful experience, most humans should not suffer too badly if stung. The best way of reducing pain and minimising the consequences of a bee sting is to carefully, and quickly, remove the shaft from the skin using your fingernail to lift it out - being careful to draw it back in the direction and angle of insertion to avoid breaking the shaft. It is important to try and remove the shaft in one piece so as not to leave part of it embedded in the wound, which can cause infection.

Observations
The images above were taken using a JVC camcorder - The GRM7 PRO, which has a special lens attachment to enable magnification of up to 110x. The wasp studied was a German Wasp (common name) - Vespula germanica(Fabr.) found in Southern England. A good way of observing insects without killing them is to place them into the freezer or ice-making compartment of a refrigerator for a few minutes. The rapid reduction of temperature will cause them to become immobile for a short period. They can then be removed and studied under a low power microscope or magnifier. Be aware that this time may not be long if you are filming them and using hot lights for illumination. If you leave them too long in the 'fridge' they will die. The best way to know how long is by experiment, starting with short times and gradually increasing the length when you have timed their recovery at room or working environment temperatures.

References and sources of information:-
Collins Field Guide: Insects of Britain & Northern Europe (3rd Edition)
by Michael Chinery. ISBN 0-00-219918-1

Destructive and Useful Insects (4th Edition)
by C.L.Metcalf & W.P. Flint and revised by R.L.Metcalf (ISBN 07-041658-3) Library of congress Catalog Card Number 61-14049 published by Mcgraw-Hill Book Company 1962.

Information relating to points indicated in Fig.1 and Fig.2 by personal observation.

Additional visual and tutorial data, including a recorded video sequence is available to registered users of Microscope for the PC software in the slideset pack called Wasp Warriors.

Maurice Smith.

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