Oh crap I though you were talking about the little roach nymphs! I'm such a doofus lmao!
I'm guessing they are either fungus gnat or phorid fly maggots, and seeing as there isn't any substrate, they are probably phorid fly larva. Any dead bodies in the cage ATM?
I doubt they are fruit fly larva as those would be in rotting fruit, and it does not look like the individuals pictured are near any fruit. And to answer your question, no, fruit fly larva are not parasitic.