with out seeing a picture I am guessing,are they in your shower by chance,they could be small slugs or If they actually have very short legs, they might be small millipedes
if that don't help let me know
have you tried bleach ,if not try that, Bleach may be the worst thing to do with cleaning black mold and mildew. While it is sometimes classified as an all natural cleaning product it is extremely harsh and the fumes are no good for the bodyand if that don't work Find the source of the problem ,you problaby don't have a exhaust fan in the bathroom which will cause high humidity and are these s on the tile and grout ,if you don't have a exhaust fan maybe get one installed and that will lower the humidity a lot ,or try safe shield organic mold cleaner
If my answer was helpful please hit the accept button,
thanks for allowing me to help
I have tried bleach. Should I completely remove the caulking, dry out the shower stall and re-caulk?
My bathroom does not have an exhaust fan, but I have no other mold anywhere in my bathroom and the amount that is present is very minimal and under the door frame, (under the framework that is attached to the marble).
I used bleach and two days later they were back.
I'm thinking you take a lot of showers and what I think is happening is the humidity is so high ,they just keep coming back because in the shower it is always moist there,I don't think it is necessary to remove the grout,unless you have taken some of it out then ok,you could do that,but I think to solve the problem would be to install a exhaust fan ,they aren't that much,if you are handy,the only other thing I can think of is going to a hardware store and ask for some thing that will kill black mold,I have seen this black mold many times in showers but never had to deal with it because I was always working on something else let bathroom sink or toilet,no one seemed concern about that,but invest in a exhaust fan and it should fix the problem ,plus your mirror will not fog up as much.I hope this was of help to you if so please press accept