Dense mayfly swarm causes crashes, closes US bridge
http://www.bbc.com/news/world-us-canada-33129833
- 14 June 2015

A dense swarm of mayflies caused motorcycle crashes and the overnight closure of a bridge in the US state of Pennsylvania.
The sheer volume of insects reduced visibility, and turned the road surface of the bridge over the Susquehanna River, in Lancaster County, into a treacherous, slippery mess.
Piles of mayflies up to 2ft (0.6m) deep were seen the morning after.
http://www.bbc.com/news/world-us-canada-33129833