or if they are more like little white wriggly worms they could be something called planaria (not sure of spelling) but these too are normal and fish will eat them - although planaria are often associated with an overfed tank I had them early in my fishless cycle of my first an now main tank - even with nasty levels of ammonia etc.
Anyway - its normal to have 'bugs' of some sort in a tank - I even have snails in my tank without having real plants and zebra loaches who are snail heat seeking missiles
The only things to be concerned about (imho) are dragon fly larvae only because they are big enough to eat small fish - your not too likely to have a problem with one of these and even if you do find 1 - just scoop it out and rehome it in the pond or river
More sinister bugs that you wont see until too late are Ich parasites - aka whitespot - so if you dont have fish yet - do some research (within our halls of course
) and get a bottle of ich treatment to have ready and always have a supply of this treatment whenever you keep fish - its a real swine and kills most fish really fast if left untreated
Dont mean to scare you - but better warned than caught by surprise
If you dont like the look of a bug or snail - you can always squish it against the side of the glass and the fish (if you have em) will eat the rest
a bit of live food/fresh food to add to the interest of their diet (it happens in nature anyway)