The approach of a wasp’s ominous buzz along with a glimpse of its black and yellow warning colours are more than enough to make the spheksophobics among us hyperventilate and break out in a cold sweat. Even without an irrational fear of wasps it is hard not to become jumpy, not to mention irritated, as the cheeky little insects with their painful stings take to drinking our lemonade and nibbling the icing on our cakes during the last few al fresco dinners and afternoon teas of the season. Luckily, much of the ill feeling towards wasps has its roots in a few basic misunderstandings, which means there is a lot of room for improvement in the often turbulent human/wasp relationship.
Wasps get a lot of bad press. Many newspapers like to feature gruesome, fear-inducing head-lines and as a result, any occurrence of death following wasp stings is bound to be featured heavily. While it is unfortunately true that it is possible to die after being stung by wasps, this is almost always as a result of a severe allergic reaction to the venom (anaphylaxis), rather than a consequence of the stings themselves. Every year, more people die from anaphylaxis caused by food allergies than anaphylaxis caused by insect stings, but this does not usually make the headlines because ‘killer peanuts’ just do not have quite the same impact on newspaper sales.
What usually remains unsaid is that deaths from insect stings are exceptionally rare. Statistically, dying from an insect sting (wasp, hornet and bee combined) is only slightly more likely than being killed by lightning. So, while it is important to be aware of the symptoms of anaphylaxis (which include swelling of the face and throat, wheezing, widespread rash/itching, vomiting and fainting) and to seek medical attention should any of these develop following a sting, there is no need to panic. For individuals who have suffered a severe allergic reaction to wasp venom in the past, immunotherapy treatment is
95% effective in preventing future occurrences of anaphylaxis.
Even without an allergic reaction, being stung by a wasp is undoubtedly an unpleasant experience. Although social wasps occasionally use their sting when hunting, they usually kill their prey by biting, their venom being primarily designed as a defensive weapon. Its purpose is to be as painful as possible for as long as possible, so that an attacker is fooled into believing a large amount of damage has been caused and is put off trying to interfere with a wasp again in the future. In order to achieve this, wasp venom is made up of a complex mixture of chemicals. Among other things, it contains enzymes that break down cell membranes and allow the venom to penetrate deeper into the tissue, neurotransmitters that cause the nerves to send pain signals to the brain and noradrenaline that constricts the blood vessels around the sting so that the venom cannot be carried away as quickly and the pain is felt for longer.
Unlike honeybees which die after delivering a sting because their barbed stings cannot be retracted and end up being torn from their bodies, wasps have a smooth sting which can be retracted and re-used. As a result, wasps are somewhat more ready to sting than bees. However, as is the case with bees, wasps only sting humans when they feel threatened. When a wasp is buzzing around at eye level, it is easy to forget that they are tiny in comparison to humans. From a wasp’s point of view, a person flailing his or her arms around trying to shoo it away from a picnic is akin to a skyscraper suddenly starting to take swipes at innocent pedestrians with its fiftieth and fifty-second floors. Under those circumstances, anyone may be forgiven for feeling startled.
Wasp larvae and pupae are soft-bodied, very nutritious and totally defenceless, which means many predators would exploit them as a food source if adult wasps weren’t fiercely protective of their nests. In fact, in a number of countries, notably China and Japan, wasp brood is considered a delicacy and tinned boiled wasp brood can be found on supermarket shelves. In order to protect their young, all the wasps in a colony will work together to fight off an attacker, and they will give chase
for some distance to ensure the threat has gone for good. Therefore, should one inadvertently disturb a wasps’ nest, the best course of action is rapid retreat, taking care not to trip and fall in the process. A swarm of wasps defending their nest is going to strike fear into most people’s hearts, but it is important to remember that even then they are not acting aggressively, they are only trying to prevent their young from being harmed.
A large wasps’ nest is the culmination of a herculean effort involving hundreds and sometimes thousands of individuals. It is started in spring by a single mated queen lucky enough to have survived the winter in a sheltered crevice. When day length increases and temperatures rise, the queen starts looking for a suitable nest site.
Depending on which species she belongs to, she will be looking for either a cavity underground, or a sheltered spot off the ground, for example in a dense shrub, attic or tree hollow (photo 1). When she has decided on a location, the young queen starts collecting soft wood fibres which she chews and mixes with saliva to create a kind of paper mache. Out of this she fashions a stalk which she attaches to the roof of her cavity or a branch or beam. At the bottom of this stalk she then constructs two upside-down hexagonal cells and lays an egg in each cell. Next she builds a cover similar to an umbrella over her first cells. Over the course of a week or so she adds more cells (and eggs) and expands the umbrella to form a ball with a small entrance at the bottom. Depending on temperature, more covering layers are added around the nest to improve the insulation. After around five days, her first eggs start to hatch. At this stage she starts collecting not only wood fibre to expand her nest but also fluids (including some nectar and honeydew) as well as food for the larvae. The larvae are fed on soft-bodied insects which the queen chews and shapes into small balls before passing them to her young.
Hunting wasps can often be seen flying slowly from plant to plant, checking each one from various angles for suitable prey. Sometimes a non-moving human is inspected in a similar manner. This can be unnerving, but the wasp will soon be on its way when it has ascertained that there are no caterpillars on the human in question.
Adult wasps are unable to eat solid food because it can not pass into their stomach as a result of their extremely narrow ‘wasp waist’ (showing particularly well in the German Wasp worker in photo 2). As a result, they are restricted to drinking sugary liquids, the body fluids of the insects they collect for their larvae, and a special sweet nutritious secretion produced by the wasp larvae themselves in their salivary glands which they feed back to the adults.
After hatching, the hind-ends of the larvae initially remain attached to their eggshells, which are firmly glued onto the side walls of their cells. This prevents them from falling out of their upside-down nurseries. After three moults, however, the larvae become too big to remain in their original position and have to undertake a precarious manoeuvre whereby they grab on to the cell wall with their jaws while carefully moving their hind end all the way to the bottom (or rather the top) of their upsidedown cell. If they manage to get into the correct position, they can then wedge themselves safely and comfortably across the cell by means of ridges on their bodies. However, should they lose their grip at any stage in the proceedings, they inevitably drop head first out of their cells. Legless, plump and less than agile, any fallen larvae are doomed to die of starvation or exposure, because it is very uncommon for a fallen larva to be put back into a cell by an adult. Usually they are regarded as debris and removed from the nest along with other bits of waste matter.
Those larvae that manage to change position successfully continue to grow rapidly and are ready to pupate after one further moult. At this stage, they spin a silken cocoon inside which they pupate. Just before pupation, the larvae release all the faecal matter they have accumulated in their unusual blind gut since hatching as one rather large pellet. Unsurprisingly, in cultures where wasp brood is eaten, the pupae are generally considered tastier than the larvae.
Depending on availability of food (growth is faster when food is plentiful), development from egg to adult wasp takes approximately four weeks. Vacated cells are usually re-used at least once. Photo 3 shows part of a large nest of the Common Wasp (Vespula vulgaris) containing healthy white larvae, some diseased black larvae, pupae in their cocoons and one recently vacated cell in which a new egg has already been laid. When the first workers emerge, they take over foraging and nest maintenance duties and the queen dedicates herself solely to egg laying, laying as many as 300 eggs a day during the phase of most rapid colony expansion in early summer. Soon, she becomes so swollen with eggs that she can no longer fly. Photo 4 shows a German Wasp (Vespula germanica) queen alongside a number of her workers. After a period of colony growth and nest expansion during which only workers are reared, the focus of the colony shifts towards raising the next generation of queens and males. Large queen cells are built near the bottom of the nest, and males are reared in the former worker cells higher up in the nest. The new queen wasps can be distinguished from the workers by their larger size. The new males are not much bigger than the workers but have considerably longer antennae (see next page – photo 5).
A similar life cycle is shared by all nine species of social wasp in Britain, including the largest among them, the unmistakeable brown and yellow hornet (Vespa crabro) (photo 6).
The four species in the genus Dolichovespula, (the Median, Norwegian, Saxon and Tree Wasps) tend to have a shorter cycle with smaller maximum colony sizes and new queens and males already emerging during the summer. Dolichovespula wasps usually nest above ground (e.g. in trees or dense shrubs) away from human habitation.
The four species in the genus Vespula (the Common, German, Red and Cuckoo Wasps) usually nest below ground, but also in other kinds of cavities, often in close proximity to humans. Two of the Vespula species, the Common Wasp and the German Wasp, have a longer cycle in which their colonies grow to rather large sizes and queens and males are not produced until the autumn. The large numbers of individuals per colony (around 3000 workers and several hundred new queens and males at the height of the season) as well as their propensity to nest in or near buildings means they are the most frequently encountered wasps.
It is easy to tell Dolichovespula wasps and Vespula wasps apart by the shape of their faces. Dolichovespula have long, pointed faces like the male Norwegian Wasp in photo 7, whereas Vespula wasps have rounded faces, beautifully illustrated by the Red Wasp worker in photo 8.
In addition to this, most British wasp species have distinctive facial markings unique to their species and (with the exception of hornets) identification requires close examination of facial markings as well as body pattern, because the latter can be very variable.
As the end of a wasps’ nest’s cycle approaches, the new generation of queens and males leaves the nest, the old queen weakens, and the workers no longer apply themselves to their tasks as eagerly as they did earlier in the season. Some workers may even start to lay eggs themselves. Workers’ eggs are infertile, but in wasps, infertile eggs are able to develop normally and become males, whereas fertile eggs become females or workers. The queen is able to produce both fertile and infertile eggs and so has the ability to control the gender of her offspring. Occasionally, workers’ eggs may mature into adult males, but usually, as the colony structure continues to fall apart, the workers start to neglect or attack the remaining few larvae instead of caring for them. With no more larvae in the nest, the workers no longer have access to their nutritious salivary secretions and need to find other ways to cover their carbohydrate require-ments. This is where our late season al fresco jam tarts come in particularly handy, though we may not be inclined to agree.
Wasps can be a nuisance and sometimes they become minor pests in orchards and around beehives, but overall they are beneficial insects, with each colony consuming thousands of invertebrates in a season. Flies and cater-pillars are among their favourite prey, which means that in garden settings they help to effectively control a number of potential pests.
Even considering this, the human/wasp relationship may never be entirely without friction as both humans and wasps are very successful, adaptable species which are bound to compete for resources (such as jam tarts and attic space) occasionally. But perhaps knowing that wasps are not out to hurt us, and that on the occasions where they try to steal our food this is only in a bid to support their young or because they themselves are starving after their colony has collapsed, makes the irritation a little easier to bear, and means fewer interactions end up having a sting in the tail.
Photos courtesy of Paul D. Brock
Paul D. Brocks’ latest bestseller A comprehensive guide to Insects of Britain & Ireland (Pisces 2014) covers more than 2100 species and has been re-printed in 2015: www.naturebureau.co.uk/bookshop/a-comprehensive-guide-to-insects-of-britain-and-ireland-detail, or call 01635 550380