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.
Yikes! That is definitely horror movie material.
Those animals are tough. I think a human would go into anaphylactic shock from that many bites due to the histamine response.
FWIW I saw a couple of WHO concerts. Definitely worth the auditory damage! :)