I’ve only seen it on video but the Caribou and Geese are harassed nearly to death by clouds of mosquitoes that at times almost obscure the lens. Some of the scenes are veritable horror movie outtakes.
I have seen them so thick that you couldn’t see ten feet away. The caribou herds spend their lives running from them. Some have scars inches deep from the repeated stings. That is scary enough, I found the sound harder to stand. One mosquito buzzing around is annoying, millions buzzing is tortuous.
The loudest outdoor concert I’ve heard was The Who in 1982. Pete Tounsend regularly experimented with their equipment to get the loudest, most clear sounds. That tour, he stacked thousands of smaller speakers and the sound travelled for miles and sounded like it would break the very concrete.
A swarm of millions of mosquitos sounds like that, only with the frequency raised to the very limit of the hearing range.