Because it prevents them from breathing, since the ant is blocking off their airway.
I'm not the greatest at grammar, but I think the very first one is incorrect. It should just be a comma, then the second just a comma as well, but the last one is correct. (I have no idea, I am sorry if you get it wrong.)
The Trojan War was won by the Greeks after a 10-year long battle. The decisive turn in the war was the charge led by Odysseus from the Trojan Horse.