Take a nosey at Slaughterbots, a fictional 7min video; https://www.youtube.com/watch?v=9CO6M2HsoIA

Ahh, I don't see how that last thing follows. I expect many expired, disabled and crippled drones lying around.

Edit: I watched to video after reading your comment. That's fucking terrifying. It's hard to make scary "action" sci-fi nowadays, and China is working hard to make dystopian sci-fi look tame, too.

Make them smaller and give them a sharp pointy end. Ask the public to name it. Reject “Stabby McDroneface” as “it sounds like a joke”. Be surprised by the first amateur reproduction. Use the moral outrage to ban all drones — even those tiny little drones that can’t life a single jelly baby. Realise drones are still useful and make and expensive license scheme that doesn’t really scale up because it’s organised with industrial era thinking instead of information era thinking. And what is old is new again.

There's already been reports of the use of toy drones for scouting and bombing in the Syrian civil war. Then there was that strange maybe-fake bombing attempt on Maduro: https://www.bbc.co.uk/news/world-latin-america-45073385

This sort of tech will probably be used to make better cluster munitions (though I wouldn't be surprised if this technology is already used in them), but I don't think there's much tactical value in this kind of tight coordination for a drone swarm. In combat you wouldn't want your drones this close together, one missile could take out a bunch of them at once.