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Sting in the tale

magazine article | Published in TES Newspaper on 18 June, 2004 | By: Ben Aldiss

Next time a wasp comes sniffing around your roof and walls, think about it as a resource for next year's teaching, says Ben Aldiss

Wasps are misunderstood. I spent most of my days for three consecutive summers surrounded by several hundreds of them and by the end of my research I was an ardent admirer. Since becoming a teacher, I have capitalised on some of the many intriguing facets of wasp natural history.

I found that wasps could play a starring role as teaching aids - and not just in biology lessons. But first, what exactly are wasps? How do they differ from bees and why do we hate them so much?

Bees and wasps are insects belonging to the order Hymenoptera, a huge group containing about 100,000 different species that also includes ants, sawflies and ichneumons (a real-life manifestation of the creatures in the Alien films, which lay eggs in insects and the grubs eventually explode out of the host body). All share the basic insect design - segmented, three-part bodies, six legs, two antennae and (usually) two pairs of wings - but they also have features that clearly distinguish them from other familiar insect groups, such as butterflies and grasshoppers. The sting is an organ peculiar to hymenopterans; most of them have the narrow "wasp waist" that separates the rear of the body from the middle part. Although the majority lead solitary lives, there are social species of bees and wasps which live in complex colonies, some of them housing millions of individuals. They share this advanced habit with only two other insect types, ants and termites.

Wasps differ from bees in some very important ways. They are not very hairy and their bright yellow and black colour is caused by pigments in the hard plates of their exoskeleton (outer shell), whereas the fluffy hairs of bees are responsible for their various stripes of orange, yellow, black and white. Perhaps you've wondered why wasps' wings look so "skinny" and inefficient? Both bees and wasps have small hind wings that are permanently coupled to the front ones by rows of tiny hooks and a groove, but while the bee's wings are noticeably broad, those of wasps are pleated in half lengthways when not in use. The two large compound eyes of bees are round or oval, but those of wasps are a curious kidney-shape.

Perhaps the most important difference of all is that of diet. Young bees and wasps are white grubs with a superficially similar appearance, but while bees feed their larvae on pollen and nectar, wasp grubs are voracious carnivores. This is one of the main reasons why wasps pester us more than bees - in the search for meat as well as sugar they are attracted by the smell of food, which they detect through their super-sensitive antennae.

They are not attracted by the smell of sugar, which is odourless, but have learned to associate the smell of sweet foods with sugar. Being designed to chew and chop their prey, their jaws are short and powerful, while the bee's mouthparts are weaker and include a long "tongue" which is brilliantly adapted for sucking nectar from tubular flowers.

Until about 20 years ago there were just seven species of social wasp - those that live in colonies - in Britain (see page 10), including the hornet, a large wasp which can fly at night. Two continental species have taken advantage of the recent warm summers and are now firmly established; with each passing year they spread further north. One species, the Median (or "Euro") Wasp has brightly coloured workers almost as large as hornets and an apparently evil temper, gaining it the unwarranted nickname of "Killer Wasp". The Saxon Wasp, on the other hand, is rather less conspicuous and has so far caused few problems.

A wasp's life is a fascinating one, full of unexpected twists. By studying a typical nest and charting its progress through the year, we can explore some of the intriguing aspects of wasp behaviour.

Queen honeybees never have to do any work other than to lay eggs. They are waited on by a huge retinue of workers, in an environment whose temperature rarely drops below 35C. Unlike those of honeybees, wasp colonies are usually annual, and the Common Wasp queen awakes in April from six months of hibernation to the daunting prospect of founding a dynasty entirely by herself.

First, the young queen (who was fertilised the previous September) replenishes her energy reserves by feeding on nectar from spring flowers.

With only a short tongue, she is restricted in the plants she can visit - umbellifers, such as cow parsley, are suitable, and a particular favourite is cotoneaster. Then begins a determined hunt for a suitable nest site.

Surprisingly, the previous year's nest is never reused and queens can be seen in late April tirelessly investigating holes in the ground or chinks in walls and buildings. Once she has discovered a suitable place to build her nest, the queen's work begins in earnest.

Whether her choice is an old rodent burrow in a grassy bank, or a cavity in a roof, she starts by flying to the nearest source of rotten wood and scrapes shavings from the surface with her sharply toothed jaws. The Common Wasp's equally common cousin, the German Wasp, chooses sound wood for this purpose and so creates a nest very different in colour and consistency. On resonant surfaces, such as wooden shed walls, the scraping can be heard several metres away on a still day.

When she has gathered enough, she moulds it with saliva before flying off to the nest site, the large ball of pulp held firmly in her jaws. In the complete darkness of the cavity she carefully makes a wafer-thin umbrella of papier-mache which she attaches to the roof. Beneath this she creates a tough pillar of the same material, onto which she builds the first 20 cells of the first comb. We still have little idea how wasps fashion such perfect hexagonal shapes in total darkness, but my research indicated that their saliva contains a pheromone (a chemical attractant). Provided the wasp returns before the wood pulp has dried, the odour guides her to exactly the right place. This papier-mache, or carton as it is more properly called, is said to have been the inspiration for the invention of paper by the Chinese in the 2nd century BC. On average, only one in 500 of the embryo nests survives to become a full colony. The reason for this is stark and simple: in the beginning, the fate of the nest depends entirely on the queen - if she dies, it dies. In this respect, honeybees are very different.

By the time she has finished building the first cells and has laid an egg in each, the queen can afford to rest awhile until the first grubs hatch.

Oddly, the cells face vertically downwards, so the eggs have to be "glued" on and the young larvae are adapted to hang on tight, to avoid falling out.

The queen's workload increases again as she has to forage for food for her ever-demanding brood of 20 young grubs. In fact she has to develop new skills - and quickly - because they clamour for meat. Hunting and killing insects is instinctive in wasps, but at first they are not very good at it and only score two successes out of every 10 attempts.

Surprisingly, the sting is not used to kill the prey: the queen patrols an area where flying insects such as flies and bluebottles can be found, then suddenly pounces and grabs an unfortunate victim in her six legs. Before it can begin to struggle, she clips off its head, wings, legs and abdomen, then chews the protein-rich thorax into a ball of meat paste and flies back with it to the nest. Every tiny grub is then fed its share - fresh fast-food to order. By mid-June, each grub has reached full size, has spun a cap of silk over its cell, turned into a pupa and emerged as an adult worker wasp.

If the queen manages to survive the first two crucial months without being eaten by a predator or swatted by a vespophobic human, the future of the colony is almost assured - her small contingent of workers takes over all the duties apart from egg-laying and the colony expands at an ever-increasing rate. From a tiny, fragile structure, the Common Wasp's nest grows exponentially throughout the summer to become a huge construction containing upwards of 2,000 adult insects by September.

The carton umbrella is repeatedly altered and rebuilt to cope with the expansion and eventually becomes a thick, spherical wall with air-pockets, enclosing the whole colony in a protective, insulating layer - a model for household cavity insulation. The first comb of cells is expanded into a circular plate and up to seven more are suspended successively beneath it, with just enough space in between for a wasp to comfortably crawl about.

Perhaps designers of multi-storey car parks got their inspiration here.

By mid-August, the nest is huge - a living machine, or "super-organism" designed with one end: to successfully nurture and release the next generation of queens, with enough males to ensure successful mating. At the height of its activity, the nest will have produced around 25,000 worker wasps and about 500 queens and males. By now the founding queen will be laying eggs at the rate of 200 per day. The temperature inside the nest is maintained at a remarkably constant 35C by "colony homeostasis". On cold days, fewer wasps venture out to forage and those in the nest huddle on the combs to generate heat. In hot weather workers collect water and spread it on the absorbent surfaces of the paper nest. Then they cling on in strategic places and buzz their wings to create cooling air currents. The evaporating water draws latent heat out of the nest. By adjusting the balance of these behaviour patterns, the wasps maintain the operating temperature of the colony at an optimum.

All workers are female, like the queen, and are capable of laying eggs, though they are too small to mate. The eggs they lay are unfertilised (like most chickens' eggs) and only contain one set of chromosones - just like human eggs. However, unlike a human egg that needs a matching set of chromosones (from sperm) to develop into a baby, wasp eggs that remain unfertilised turn into male wasps. A fertilised queen egg develops into a worker wasp, ie female.

So why does a queen develop instead of a worker?If the egg is laid in a larger cell than those the workers are laid in, and that grub is fed more than the worker grubs, a queen is the result because the size they grow to is not restricted, unlike the workers reared in the smaller cells. This means that, even if the queen dies early in the life of a colony, the situation can be salvaged. As soon as the workers detect the death of the queen (the influence of her pheremones is no longer felt) they do two things: first they increase the size of some cells already containing developing worker grubs, then they feed the grubs more food to turn them into queens. Next, the workers being to lay eggs (unfertilised) and a month later these eggs have developed into male wasps at the same time the queens hatch from the enlarged cells. The colony has now achieved its aim.

Until mid-August, all the wasps in the colony are female, but then their behaviour alters and the workers start to build larger cells. As yet we still do not know what triggers this. The queen lays unfertilised eggs in some of these larger cells to produce males. It is likely that workers also lay unfertilised eggs at this busy stage of colony expansion. In some of the other large cells, the queen lays fertilised eggs, which become queens.

By September, the new queens and males begin to stream from the nest on their mating flights and the social structure of the colony suddenly begins to crumble. It is probable that the coherence of the organisation prior to this is maintained by a complex balance of pheromones, mostly secreted by the founding queen. When the queen's job is over and her body begins to wear out, this cocktail of chemical cues falters and can no longer exert its control over the behaviour of the workers. Anarchy reigns and the remaining workers go berserk, forsaking their duties and hauling the hungry larvae out of their cells to die some distance from the nest. This phase - the so-called couvain abortif - signals the end of the colony and by the time the first hard frost hits, all activity has usually ceased. The old queen, her workers and the males all die, leaving just 500 newly mated queens to feed up for winter and go into hibernation. Next year the cycle will turn again, just as it has for many millions of years.

Resources

Wasp nests are relatively easy to collect if they have been built in sheds or roof spaces. As they are never used twice and all the adult wasps die in the winter it is perfectly safe to remove old nests in January or February.

Cut the nest free using a long-bladed knife. The colony can then be cut vertically in half (use a sharp knife in a sawing motion) to show the insulating envelope and the layers of combs inside. The other half can be teased apart to demonstrate the structure in more detail. Note the geometry of the combs, the different textures of the carton and the stripes of variously coloured wood pulp applied by different worker wasps.

Websites

The Anaphylaxis Campaign (information for those hypersensitive to wasp stings): www.anaphylaxis.org.uk

Essex Wildlife Trust (this and other county wildlife trusts have useful leaflets and online information about wasps and bees): www.essexwt.org.uk

Northamptonshire Beekeepers' Association: www.northantsbees.fsnet.co.uk

Bio-Images: the Virtual Field Guide (a useful site containing images of wasps and other insects): www.bioimages.org.uk

Britain's social wasps

* Hornet - Vespa crabro

Size: 19-35mm

Reddish-brown and yellow with brown wings. Colony medium-sized, usually in hollow tree. Found in southern England, as far as Yorkshire

* Common Wasp - Vespula vulgaris

Size: 11-20mm

Black and yellow, with black, anchor-shape on face. Colony large, usually underground, but often in roof-spaces. Found all over Britain

* German Wasp - Vespula germanica

Size: 10-19mm

Black and yellow, with black spot (or triangle of three spots) on face.

Colony large, usually underground, but often in roof-spaces. Found all over Britain, except north-west Ireland and north-west Scotland

* Red Wasp - Vespula rufa

Size: 10-20mm

Black and yellow, with red on front of abdomen. Thick, black, vertical line on face. Colony small, underground. Found all over Britain, but commonest in extreme south and west.

* Cuckoo Wasp - Vespula austriaca

Size: 15-20mm; no workers (only queens and males). Black and yellow, with two or three black spots on face. No colony - social parasite in colonies of Red Wasp. Rare and mainly found in north and west Britain.

* Median Wasp (also known as 'French', 'Killer' or 'Euro' Wasp) - Dolichovespula media

Workers of assorted sizes (10 - 25mm) and colours - some standard yellow and black, some almost pure black, others yellow, black and red. Colony medium-sized, hanging from a branch, often in garden shrubs or hedges.

Founding mainly in southern Britain, but spreading north rapidly.

* Tree Wasp - Dolichovespula sylvestris

Size: 12-22mm. Vivid yellow and black with clear yellow face, or with single black spot.

Colony small, usually hanging from a branch, but sometimes in bird nest-boxes or other wooden containers. Found all over Britain.

* Norwegian Wasp - Dolichovespula norvegica

Size: 10-19mm. Black and yellow, with red at front of abdomen and thick, black, stripe on face. Colony small, usually hanging from a branch, but sometimes under ground. Found all over Britain, but rare in the south.

* Saxon Wasp - Dolichovespula saxonica

Size: 11-17mm. Black and yellow, often mainly black, with irregular black stripe on face.

Colony small, usually hanging from a branch, but often in sheds and roof spaces. Found mainly in south Britain, but spreading north.


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