Catch one in a cup or plastic bag and stick it in the freezer for about 10 minutes. When you take it out it will look dead, but it's not (unless you leave it in too long.) Being careful not to rip it's wings off, tie a small string or fishing line to one of it's legs.
In a few minutes it will thaw and start to walk around, and then start to fly. You can now walk it around the park like you were carrying a balloon.
I think repeatidly slapping them with a pretty soft plastic attraption until they stop moving is even harsher though.
Or slapping them outta the air, trying to electrocute them but having too little power on the shitty device so only their wings get burned.
Or vacuuming them up
Or flushing them down the drain.
Honestly, whatever people usually do to them it's way way crueller
It's soft to you, not to the fly. You don't slap a fly "until it stops moving". When you swat a fly, it explodes.
Don’t Google dust mites.
Because of their rarity, I find that the ones that wear tiny top hats are easily distinguishable too.
The next day, same story. The flies were now appearing throughout the day. They all looked the same. Where the hell were they coming from? The windows were still closed. I kept vacuuming.
Eventually things were starting to get very irritating. I hunted for an entry point for days without finding anything and the flies just kept on appearing. I was pretty good at vacuuming flies by this point.
By day six I spotted a group of them hanging out near my Kentia palm. Aha! A fly had laid eggs in the soil of the plant. I had no idea that it was a suitable food source for larvae. Needless to say I quickly filled it with gravel and I guess that's the story of how I became a qualified Fly Detective.