During flight, a wing produces lift by accelerating airflow over its upper surface and, in some fixed wing flight, accelerated air can, and does, reach supersonic speeds, even though the airplane itself may be flying at a subsonic airspeed.

Helicopters stay up because, even though the body of the aircraft can be stationary, the wings rotate fast enough to provide lift in a manner similar to fixed wing aircraft.

Airborne insects can be likened to revolving propeller bladed aircraft because their wings generate lift by steadily pushing air downward.

Therefore, if, like helicopters, hovering insect flight is possible because of the high speed of their wings despite the static position of their bodies; then do really high speed wing flappers, e.g. hoverflies, also ever accelerate upper wing surface airflow to supersonic speeds?

If this is the case, then how do these insects avoid creating small sonic booms? Or if they don’t, then why don’t we hear them? Or maybe we do? Maybe the irritating whine we hear when listening closely to something like a hoverfly, is actually a series of really tiny sonic booms merging into one long hum?

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References:

https://en.wikipedia.org/wiki/High-speed_flight

‘Airplane Flying Handbook’ (2004). U.S. Department of Transportation Federal Aviation Administration Flight Standards Service

Sanjay P. Sane: ‘Induced airflow in flying insects I. A theoretical model of the induced flow’

If you want to make a Greek laugh, ask them to say the name for mermaid in their language and then try repeating it back to them. I’ve tried many times and never once succeeded in getting it right. The word begins with a sound somewhere between a gurgle and a rumble, as far as I can understand made at the back of the throat, proceeds to a short ‘o’ (omicro?) before transitioning to a roll not dissimilar to the starting growl, (unless you’re Greek, in which case I’m sure it sounds completely different, actually you can sort of tell its a bit different too though it’s hard to say how) this part of the word involving something like tongue rolling, but not quite the way you might pronounce a rolled ‘r’ – especially not a French ‘r’. But in any case, you’ve hardly had time to get your tongue around that before you’re back into trying to pronounce the first gurgle again, then leaving that behind to try your hand at a longer ‘o’ ( though despite it being longer it isn’t omega) finally to reach the familiar phonetic safety of ‘na’ to finish off. The whole procedure should, despite the complexity, take only a fraction of a second to accomplish.

By this point in time your friend will be creased up with laughter and begging you to have another go.

Written down, the word gets even more interesting, because γοργόνα, transliterated into western script, is ‘gorgóna’ and you immediately think to yourself (well I did anyway) that’s Gorgon, not mermaid, and is there a connection between women with snakes for hair and those with tails instead of legs? Apparently, the name derives from the ancient Greek word gorgós, which means ‘dreadful’. Well, the name does, but mermaids are more closely related to sirens (σειρήνα), because of their behaviour, i.e. using their beauty and songs to lure sailors to their deaths – only why ‘gorgóna’ then, why not something similar to siren?

You can try this argument on the Greek you’ve been speaking with, but like as not he’ll just reply: “go on, say it again”…