In my travels today I drove thru Princeton NJ. There was a brood getting off something fierce!

 I'm exaggerating but to describe the scene I would tend to use words like "tons" and "deafening".

 Within the last decade there was a similar hatching-tons of them accompanied by a deafening, eerie ,medium high pitched drone. Sounded like that distant drone you heard in the sci-fi movie with the giant radioactive ants.

 John