Insect Expert Explains Why Flies Rub Their Creepy Legs Together

While I’m terrified of daddy longlegs (even learning that they’re completely harmless hasn’t helped), I’m a bit more tolerant of spiders and flies.

There’s one exception, though. I do not like it when bluebottles sit on my windowsill, rubbing their creepy legs together like they’re plotting my downfall.

Of course, that won’t be the real reason behind the movement. But to be honest, I had no idea what was – until recently.

Speaking to The New York Times, Dr David Grimaldi, entomologist and curator at the American Museum of Natural History in Manhattan, explained they’re actually strategically grooming themselves.

“Flies have chemical receptors not just on their feet, but on their legs, as well,” the expert said.

This means they can literally taste the surface they’re on ”with their feet, and so they have to keep them very clean”. Oh, good.

A little bit like cats’ tongues, BBC Discover Wildlife added, flies clean themselves with comb-like bristles on their legs.

Aside from helping them to perceive the world around them more accurately, it can also keep them aerodynamic, as grit and pollen can affect how insects and flies move through the air.

And flies don’t just rely on the “taste” from their legs to help them orient themselves.

They also need their antennae and the tiny hairs on their bodies and heads to stay clean in order to keep their receptors accurate, and to help “detect air currents and monitor body position” while flying.

That’s why it seems like flies sometimes “wash” their head with their forelegs, too.

When you think about flies rubbing their legs together, chances are you imagine that gleeful-looking “hand rub”-style motion.

But AZ Animals shared that “they rub their little legs against different parts of their bodies to clear any debris from the previous item they touched”, too.

That’s because debris, dust, particles, and pollen can cling to their legs when they eat or simply land on a new surface.

Entomologist Richard Jones also wrote that these minute specks can “provide a foothold for potentially deadly moulds and fungi to attack” – no wonder flies are so keen to brush them off.