Weird larvae in my hermit crab habitat...help!!!?

I have had a hermit crab for about eight or nine months now, and three times a day I wet the log in its tank, wet its sponge, change its water bowl, and mist the whole tank. Well today, when I took the sponge out of the cage to wet it, I noticed tiny little worms on the sponge!!! They weren't on the sponge last night, and they were very small and hardly looked like they were even alive, but I'm still worried. I did some research, and they look like either fruit fly larvae or gnat larvae. I'm not sure what to do...Should I wait a few days and see if they appear anywhere else in the tank again? Some sites suggest I bathe my hermit crab in salt water...but how do I do this? I'm totally clueless!! Help!!!