Parents are being warned to make sure they drain their paddling pools when they aren't being used or risk a swarm of horseflies which have a painful, dangerous bite.
The number of calls to the NHS over horsefly bites has doubled year on year, with 9,000 last week thanks to the recent heatwave.
And paddling pools can be an ideal breeding ground for horsefly larvae. The British Pest Control Association (BPCA) has now advised people to remove standing water, including paddling pools, from their gardens.
Natalie Bungay of the BPCA said: “After a prolonged period of hot weather, or rather without cold and uncomfortable conditions for invertebrate pests, insect numbers may see an increase and infestations can develop if left alone.
“This, for some invertebrate species, is more likely to be rural locations, which will generally have more available breeding opportunities in ponds, marshes and other types of standing water.
“For blood sucking insects such as horseflies, the countryside also gives access to food sources, mainly cows and horses grazing in fields.
“Horseflies and mosquitoes are interesting because they rely on aquatic larvae in wet and marshy areas, which won’t have necessarily dried up yet, even after the last four weeks of hot and dry weather conditions.”
“Horsefly bites are particularly painful because their main food source is livestock, which have a limited ability to move the fly away.
“This means they can take their food without having to worry about delivering a painful bite, as the animals are generally powerless to stop them.
“This is as opposed to mosquitoes, which extract blood through a painless bite.”
Horsefly bites are painful as the pest take 'a chunk' of flesh, unlike mosquitoes which have a relatively painless method for draining blood.
The bite can become infected and itchy, swelling and taking days to heal.
The effects of an infected horsefly bite can include a raised and nasty rash, dizziness, shortage of breath, and weak and swollen limbs.
Current treatments include antihistamine and steroid creams and in serious cases, broad-spectrum antibiotics.
Dr Nick Scriven, president of the Society for Acute Medicine, told the BBC : “We wouldn’t normally see anyone coming to hospital for a bite, but we have seen a few recently needing treatment with antibiotics, which is very unusual.
“A couple of these were infected bites from horseflies. They actually give one of the nastier bites, because they take a chunk out of you.
“They can be very painful, and can take a while to heal, and as result can get infected and need antibiotics. In the worst-case scenario, they can cause cellulitis, an infection of the skin.”
NHS guidance advises visiting your GP if an insect bite results in symptoms of an infection such as pus, increased pain, redness and swelling.