A swarm of sand flies.[1]
They do kill by sucking them in the sand. people wouldn't breathe
There are about 700 species of sand flies of which about 70 are taken to recognition that they can transmit diseases.
Sand flies can bite a person anywhere on the persons body. A person can use sprays to avoid being bitten by the flies.
turn you into a mermaid or kill you
Blood
Borax will kill fruit flies. Place some yogurt in the room with borax in it and it will kill off the flies.
Sand is not alive, so urine cannot kill it. However, some creatures like small crustaceans burrow under the sand. It would take a LOT of urine to kill one.
You kill the sand giants
Flies themselves don't kill people, but some flies may carry diseases that do.
They kill flies and other small insects to feed their larvae.
Sand is not good to eat. Small amounts won't hurt.