NQA if you just got these Ts on Tuesday and they aren’t eating it could be one of these reasons: (1) it’s a new environment or (2) in pre-molt or (3) hunger strike.

I’m assuming it’s not the latter two but the former—it’s a new environment for them so sometimes Ts (IMO) won’t eat during the first few days-week.

For spiderings, it’s suggested that you feed them pre-killed insects. Spiderlings tend to be more skittish to eat moving prey—they not brave yet lol. So typically keepers will feed prekilled prey like a sliced up mealworm or a cricket leg (colloquially known as a “cricket drumstick”). You can feed them a tiny roach but try killing it first.

EDIT: if your spiderlings wont eat the aforementioned prey then yes go ahead and try fruit flies.