A swarm of mayflies in the US state of Illinois has caused traffic chaos after they were stacked six inches deep (15cm) on a bridge.

Mayfly swarm on a bridge in Illinois.

Mayfly swarm on a bridge in Illinois. Image by Press Association

The Havana Police Department posted pictures of the insect “invasion” on its Facebook page – look away now if you’re not a fan of creepy-crawlies – as they warned drivers to take care after a motorcyclist had been involved in an accident.

Havana Police Department

Residents woke up to the unlikely travel hazard with the police’s warning stating the road had become “very slick” after the insects had been run over. Such was the problem that some cars had been stuck in the middle of the bridge – we’re guessing they simply couldn’t see through their windscreen – so we shudder to think how it was to be travelling on a motorbike.

Look at the size of those things!