Why Does My House Suddenly Have So Many Flies?

A week ago, my house was pretty much fly-free. But something’s changed since: now the sun’s out, it feels like every insect in the country has made its many-legged way into my home.

Well-fed bluebottles buzz lazily through my living room. Mosquitoes (we’re not even near a body of water!) flit menacingly. I think I’ve even seen some fruit flies, which are usually most prolific around August.

I’m not alone. Colleagues and friends have noticed the unexpected visitors, too.

What’s going on? Do we just notice flies more when it’s hot out? Or does their behaviour actually change?

We put those questions to entomologist Professor Richard Wall from the University of Bristol, and also asked how to get rid of them.

Professor Wall said that there’s a pretty simple explanation in this particular case: “if people see more flies in their houses when it’s hot, it’s probably because they have the windows open more”.

We’ve experienced something of a temperature whiplash recently, as the weather swung from relatively cool to record-breakingly hot this month. That means that while you might have been trying to keep the heat in as recently as last week, you’ve probably inadvertently given flies a new way in since.

Outside of this specific situation, the expert added that heat really can change how the creatures act.

“Flies do… breed faster when it’s hotter,” he told HuffPost UK.

However, that’s not what we’re experiencing now, as “it takes weeks or months to get a noticeable increase in numbers”.

Stopping them from getting in in the first place is the most important step, Professor Wall said.

“The only real way to make your house more fly-free is to install mesh screens over the windows and doors,” he told us.

And the expert said to steer clear of chemical controls, too: “The use of insecticides should be discouraged”.

The Wildlife Trusts said that the UK’s insect populations have “drastically declined” in recent years. We’ve lost about 50% of our bugs since the 1970s, they added, calling for the UK government to “phase out the use of pesticides in publicly-run spaces”.