Val, how old is your tank? If your tank is fairly new than I would think some kind of Hydroid. Are they white and have a pen size body with what looks like legs all the way around, move very slow clinging to the glass of your aquarium? Then I would say Hydroid.
If your tank is a few months old and they look like insects and move very fast then I'd say copepods.
Either way I wouldn't worry.
Need a pic to be sure though. I could be way off in left field.
Shane