Don't be caught by the buzz this month

We may be hoping for an Indian summer, but warm autumn weather means an extra lease of life for Britain's wasps and hornets. Insect expert Ben Aldiss explains how to avoid feeling the sting

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After an unspectacular couple of months, notable more for a lack of sunshine than a surfeit of it, most of us would welcome an Indian summer. There are some though – an estimated 150,000 in the UK – who would view such a prospect less enthusiastically. These are the unfortunate individuals who are hypersensitive to wasp and hornet stings.

Although no one likes to be stung, the effects are generally local and transient, but for a person who is unusually allergic to the venom of bees or wasps, a single sting can be fatal.

Luckily this hypersensitivity is not instant, taking months or even years to develop, so the victim generally knows that he or she needs to take care in the wasp season. The big problem with wasps, as opposed to bees, is that they are attracted to us and our foods with a persistence that is legendary – bees are more interested in flowers.

Calm, sunny weather in September provides the ideal opportunity for wasp colonies to reach their peak size and to achieve their purpose: the release of thousands of virgin queens and males to ensure the continuity of the species in the following spring. No wonder some people dread the thought of good weather at this time of year.

So is 2011 a bumper year for wasps? And if it is, what can we do to avoid being stung?

In the late 1970s I spent three years doing research on wasps for my PhD. At the time, there were just seven species in Britain, including the biggest of them all, the hornet. I was financed by two sponsors, each with rather different agendas. The Science Research Council requested me to find out why wasps sting. Rentokil, on the other hand, had a more mercenary aim: how to attract wasps away from jam and chocolate factories.

My technique for investigating the first problem involved probably the cheapest and simplest apparatus ever used in a scientific research project: balls of cotton wool attached to two lengths of bamboo, which I dangled in front of wasps' nests until they were attacked. Using a binocular microscope and extremely small dissecting instruments I had made from pins and matchsticks, I gradually isolated the source of a chemical in the wasps' bodies that was responsible for eliciting the colony defence response. It came from the venom sac – a tiny bag the size of a pinhead.

Back at the Chemical Entomology Unit of Southampton University, I analysed the venom and found a chemical called N-3-methylbutylacetamide. Being just the right size and volatility to evaporate at the nest entrance, this molecule was the perfect candidate for an alarm pheromone – a chemical that rouses an animal to the heights of aggression, then homes it in to attack, as precisely as a kamikaze aircraft hits a warship.

But this was not the full story: the alarm pheromone was the main stimulus, but something else was needed to induce the most frenzied responses. After many similar experiments, carried out at varying distances from the nest and using different colours of cotton wool, I was able to show that the fiercest attacks occurred within five metres of the colony, against black or dark-coloured cotton wool that was moving rapidly. White cotton wool, held motionless, provoked hardly a reaction, even when doused with the pheromone.

Wasps forage for meat to provide their larvae with protein, and collect sugar for their own energy needs. For these two foods they will fly 500 metres or more from the nest. Here, where there is no danger to their colony, wasps fend for themselves and will only sting in self-defence – if we flap at them or they get trapped in our clothing, for instance.

So now for the answers to the two questions posed earlier. Yes, 2011 was looking bad if you are afraid of wasps. Balmy weather this time last year meant more insects for wasps to feed to their young, so more queens to start up new colonies this spring. The icy winter provided perfect conditions for hibernation, with the result that a greater number of queens survived than in warm, wet seasons. Most colonies die in cold, rainy springs, so the exceptionally dry April allowed unprecedented numbers to flourish. Luckily for us, the poor summer weather came to the rescue – wasps don't thrive in such conditions. How can we avoid being stung? Be careful if you are near a wasps' nest – you only have to be stung once for the other wasps to smell the pheromone and home in to attack. If you are gardening, take care when pruning hedges – the so-called Euro- or killer-wasp makes its nests in these. Ideally wear white clothing and don't make fast, sudden movements. Leave the pruning until November when all the wasps will have died. If you are not near its nest and a wasp lands on you, try to keep still – it will fly away eventually. If it gets into your clothing, try not to move – allow the wasp to crawl freely out again.

Dr Ben Aldiss is an adviser in biodiversity and education for the Heritage Lottery Fund and assistant editor of the journal 'World Agriculture'

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