"Bored, angry and drunk" German wasps could start attacking and stinging people in Sheffield at random, experts have warned.
People are being warned to watch out for swarms of the insects which are now at their angriest - and most likely to sting for no reason.
Pest control chiefs says the German wasps - called yellowjackets and whose Latin name is Vespula Germanica - can give a much nastier sting than the common wasp.
The worker wasps, which are bigger than normal wasps but smaller than hornets, have now finished their work’supplying the queen wasps with nectar and have nothing to do.
The queens have now finished laying their eggs and have left the nest, meaning the worker wasps are no longer tending to the queen and are instead getting drunk on fermenting fruit.
At this time of the year - especially as the UK continues to bask in a summer heatwave - worker wasps feast on fermented fruit, meaning they are tipsy and extra bold.
Pest control firm Cleankill Environmental Services say people should be wary of the German wasps - which can sting repeatedly - at the moment, especially when having picnics or barbecues.
Boss Paul Bates said the wasps are now at their "most aggressive and dangerous" and are "particularly active" at the moment - and warned that if you try to swat a solitary wasp, it could "call for back-up" and you could end up being attacked by a swarm.
He said German wasps - which can be distinguished from normal wasps because of their size and three black spots on their face - were "causing the most problems" at the moment.
Speaking this week, he said: “The type of wasp causing most problems is the German wasp which gives a particularly painful sting despite its size.
“Worker wasps have finished their life’s work as queen wasps have stopped laying and don’t need food bringing to them.
“This means that the workers are free to go out and enjoy themselves which includes stealing meat from the barbecue.
“There will also be drunk wasps around who have been feasting on fermented fruit and will be extra bold.
“All this means that the wasps are likely to sting for no reason and they are now at their most dangerous.”
He added: “The advice is to stay calm around the wasps.
“If you agitate them, they send messages to other wasps that they are under attack and you can end up dealing with a swarm.”
He gave advice to Brits planning barbecues and parties, adding: “If you are having summer barbecues be aware that you may attract uninvited guests to the table.
“Be particularly careful if you have small children as we’ve heard some horrific stories involving children being stung.
“It’s bad enough if you are stung as an adult, but wasp stings are even more excruciating for children.”
An average nest contains 10,000 wasps, although some can house up to 500,000 and there are around 240 BILLION common wasps in the UK.