Wasps are normally associated with late summer and early autumn when they become a nuisance at picnics and barbecues.

But a high number of wasps have already been spotted in urban areas - and last year’s heatwave may be to blame.

It's all because wasp populations probably experienced a boom during last year’s hot summer, says Dr Tomás Murray, senior ecologist at the National Biodiversity Data Centre.

"I can completely believe that wasp populations did very well last year," he says.

However, Dr Murray stresses that he cannot say how well the wasp populations have done because there is no data compiled on wasp numbers year-on-year in Ireland. "We have no baseline information on wasps in Ireland," he says.

He explains how a boost in plant growth helps wasp colonies. "At the start [of the heatwave] when there was an enormous amount of [plant] growth, it definitely did benefit wasps, which means that they probably produced more new queens and males last year who mated and then those successfully mated queens are the ones who survived over winter to produce this year’s crop.

"For this particular year, they did benefit," says Dr Murray.

"The climate has definitely got to be a factor," agrees Richard Faulkner, Advanced Technical Field Consultant with Rentokil.

"Because they [insects] would have been abundant, it allows the wasp colonies to grow exponentially and grow quicker and so they can have larger numbers. So from that point of view, you’re going to get more wasps and you’re probably going to see larger colonies," says Mr Faulkner.

Mr Faulkner said that fly activity this year is "already through the roof".

"Compared to last year, we’ve had a 34 or 36% increase in fly activity in the first quarter alone," says Mr Faulkner.  

Queens are currently scoping out nests for new colonies

The wasps that are out and about at the moment are the queens. They are busy preparing the nests for the new colonies this summer.

Mr Faulkner says that the queens have probably been emerging from hibernation since late February because it has been so mild.

"The queens emerge from where they have been for winter, which could be in your attic or in the bark of a tree or a log," says Mr Faulkner. "They’re going to start making their nest out of wasp paper," he added.

Wasp paper refers to the way the nests are made. The wasps collect wood fibres which they then mix with saliva to make ‘wasp paper’. They then build the nests with layers of this paper.

What happens when a wasp stings?

There are a number of varieties of wasps in Ireland, but the ones that people would be most familiar with are known as paper wasps or social wasps. Like bees, wasps sting when they feel threatened but - unlike bees - wasps do not die after stinging.

According to the HSE, the wasps inject venom into the skin when they sting which can be sore and usually causes a swollen red mark to form on the skin.

And while most people will have a mild reaction to the sting, a very small minority of people are at risk of experiencing a severe allergic reaction that requires immediate medical attention.

Dr Murray says we also notice wasps more in urban areas as they find a lot of their food sources around bins.

"That’s why we see slightly higher densities in urban areas. Just because we’re seeing loads in urban areas, doesn’t mean the numbers have gone up nationally," says Dr Murray.

However, Dr Murray feels that wasps are "much maligned".

As well as keeping fly numbers down, wasps also pollinate some flowers.

"Wasps are brilliant because they do a little bit of pollinating and they are fantastic pest controllers because they take away a lot of garden pest insects," say Mr Faulkner.

Bumblebee numbers suffered losses during heatwave

Interestingly, the heatwave hasn't been as beneficial for other insects - last year was one of the worst years for bumblebees with a 17% drop in numbers.

The National Diversity Data Centre began monitoring bumblebee numbers in 2012.

"It was really quite dramatic," says Dr Murray of the drop in numbers last year.

The bad snow storm in March last year combined with the summer drought "really did not benefit bumblebees".

Bees are vital for biodiversity and on Thursday, Ireland became only the second country in the world to declare a climate and biodiversity emergency.

The United Kingdom became the first country to declare the emergency earlier this month, on 1 May.

Conversely, butterfly populations by comparison did really well during last year’s snow storm and long, dry summer. Their numbers went up by 29%, says Dr Murray.

Similar to butterflies, wasps undergo a metamorphosis in their life cycle. The queen begins a new colony in the spring by laying eggs which hatch into larvae. The queen will then begin collecting insects to feed the larvae. Those larvae pupate (make cocoons) and when they emerge, they will be the first workers who take on the duty of building the nest and feeding the larvae.

Why do wasps become a nuisance in late summer?

At her peak, the queen can lay between 200-250 eggs a day. Eventually new queens are born and the old queen dies off. This usually occurs in late summer. But because there’s no more larvae to feed at that point, the workers have nothing to do.

That’s the point in the year when they become annoying.

"What used to happen was that a worker would go out, kill an insect, bring it back, feed it to the larvae and the larvae would excrete this sweet droplet, a sort of payback effectively for the worker and encourage them to come back and keep feeding them," explains Dr Murray.

"It’s only when their colony collapses and they’re coming to the end of their life cycle and they’re craving a replacement for that sweet droplet that the larvae used to give them - that’s when they’re annoying us at picnics.

"That’s when they’re out interacting with us the whole time. It’s not like they’re specifically targeting us in anyway," says Dr Murray.

The wasps are simply hungry. So to discourage wasps from building nests in gardens, Mr Faulkner said it is all about "good housekeeping procedures".

He said homeowners should be vigilant and check their garden sheds for early-stage nests. He said they are ping-pong ball sized to start with and are usually located at ceiling height.

He advises homeowners to keep bins clean and away from the house to minimise wasp activity.

"If we’re going to have a fantastic summer again then a lot of people are going to be dining al fresco and [doing] a lot of barbecuing. So it’s just really ‘clean as you go’," adds Mr Faulkner.