I have found swarms of thousands of dead sand ants in front of my stoop for the past 5 days, what is going on?

They are all squirming and almost dying and everyday i sweep them up only to find another swarm of sand ants dying on my stoop the next morning. there are no ants crawling around during the day but the next morning, they are thousands of these dead ants on the verge of dying on my stoop. its been 5 consecutive days of this now and terminix came today but counldnt even tell me why this is happening. Anyone know why this is happening? HELP?