parisites

Question
i have a problem with my tank i have a 100 gallon freshwater tropical tank.On the side of my tank there is little worms that attach themselves to the side they are very small but vary in size and you can see them moving there seems to be a ton!I have a puffer fish that eats snails maybe parasites from those?Is it natural organisms got out of hand or parisites that will develop into some thing harmful to my fish?Are they living inside them ??please help thank you for your help.

Answer
are they white?
If they are small white worms about a few millimeters and they crawling along the glass:  These kinds of worms  are either flat or roundworms. Neither of these worm are bigger then about 5 millimeters. Neither type of worm will harm your fish or your plants. They are there basically because there may be extra food (nutrients) in the tank or tank water.  The population is controlled by a good tank cleaning and maintaining proper feeding volume to your fish... feed no more then what they can eat in about 3 minutes. I feed my fish twice a day.... I have a tank that is taller then wide and I have these little white worms in there.  They bugged me for quite some time before I realized that they are natures way of helping me keep my fish healthy... so now I just live with them... dave