There are many species of ants, some of which the darts might be attracted to eat and be able to ingest, and others that might just invade your vivarium and make a mini ant farm out of it, or at worst, possibly do damage to your frogs. Without a queen, it wouldn't persist forever, but I wouldn't want to introduce anything I didn't know for sure the frogs would lap up and digest. Fruit flies are safer and much easier as a staple.
Until someone does some extensive research on just which species of ants dart frogs will and can eat, I'm playing it on the cautious side. Maybe putting in a single ant to see what happens is O.K. Each ant specie is very different in habit from every other. Some cut leaves and grow gardens of mold, some feed off honey pot ants, some get drunk on beetles that live with them as parasites and exude alchol like the local saloon, some go on marches and devour everything they come across. Some bite and cause pain from formic acid. Some make slaves out of a different specie. Some invade houses, marching in a line and go for the sugar bowl or fruit. Some eat living flesh. So an ant is not an ant is not an ant, to paraphrase negatively "A Rose is a rose is a rose." I'm content to let some grad student do his research on what kind of ants are good for dart frogs to eat before I try it full scale.
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Patty
Lost River, Idaho
4 D. auratus blue
3 D. galactonotus pumpkin orange splash back
5 D. imitator
4 D. leukomelas
4 D. pumilio Bastimentos