I threw in some shrimp last night and they tore into it. A while later I tossed in some more. I'll see if there's anything left alive in the tank when I get home tonight. lolYes those are nassarius and they are probably hungry and there isn’t enough food for them since it’s a new tank. I’d recommend burying some food like pellets in the sand. And no they shouldn’t kill or eat other snails they could have been dead already.
Gotta admit, I wasn't expecting Bloodthirsty Cannibalistic Killer Snails.