Lovers of the outdoors have been warned of a sharp rise in hospitalisations and deaths from wasp, bee and hornet stings.
Britain had seen a rise in an aggressive species of wasp
Latest official figures show 843 people were admitted for medical care for stings in 2004/5 compared to 369 in the previous year.
Experts say the sudden increase could be due to a new invasive species of aggressive wasp from the Continent.
Advice is to take extra care to avoid stings, especially if you are allergic.
Professor Lars Chittka, an expert in behavioural ecology at Queen Mary College, University of London, said Britain had seen a rise in an invasive, aggressive species of wasp, called Dolichovespula media, in recent years.
If you are allergic, carry your medication
Seek medical attention immediately if you have a bad reaction to a sting
Move slowly and calmly in order not to aggravate wasps
Check your food for wasps before you take a bite
Get a professional to remove any insect nests
"Likewise hornets are spreading quite a bit. To what extent these two species are responsible for the hospitalisations I do not know. But certainly if there are more of these stinging insects then there is more chance that they will contribute to it."
He thought it was unlikely that hornets would be the main culprit.
"Hornets look very threatening, they are very big and noisy but unless they are disturbed near the nest they are actually quite docile. They don't usually attack.
"The Dolichovespula is a slightly different story because they are reasonably aggressive and they build relatively small nests in trees and bushes at eye height."
He said this meant that gardeners could easily stumble across the nests and be attacked.
"That happens quite commonly because the wasps patrol on the surface of the nest and then fly in the face of people who come too near."
He said last year's death and hospital admission figures for stings, gathered by the Information Centre for health and social care and the Office for National Statistics, were outstandingly high.
Eight people died from insect stings in 2004 compared to an average of two for the previous four years.
Professor Chittka said: "Whether that trend continues this year is hard to say. By my own feeling I have seen fewer wasps this year than many others so I think it is unlikely.
"But usually most events happen at the end of summer when people are out and about and the wasp colonies are at their peak size and the wasps can't find as many natural food sources and turn to our ice-creams. That's when people have unpleasant encounters with them."
Although most stings were relatively harmless, some can be extremely dangerous and even deadly.
Bites in the throat and mouth can swell and compromise breathing. Some people are highly allergic to stings and can go into shock and die without treatment.
Experts advise that people do their best to avoid stings. Those who know they are allergic to stings should carry their medication with them. Anyone who is stung and develops a bad reaction should seek immediate medical attention.
Professor Chittka said: "The symptoms are pretty clear. People will feel dizzy, they might get hives all over their body outside the site where they were stung and they might have breathing difficulties. The important thing then is to get medical attention immediately and not to delay. If you wait too long you might die."
He also gave some practical advice on how to avoid stings.
"All stinging insects are most aggressive near their nests. If you find a nest, get someone professional in to exterminate it rather than trying it yourself.
"If there are wasps in the area and you are eating, look at what you are about to take a bite of.
"Also, don't flail your arms at the wasp. Instead make slow and calm movements."