I agree with Terry, looks like a Green Frog to me as well.

Slugs will probably be a hard sell as food since they don't move very fast and frogs go for living and wriggling prey items. Earthworms are a good choice (and infinitely better as a staple diet over mealworms), but you might want to try putting them on or in something hard (like a small plastic dish) so the frog doesn't have to chow down a bunch of the substrate with it and to keep the worms from burrowing. Or try hand feeding by dangling the worm with tweezers, but your frog might be too skittish for that to work.