hiya, i have a yellow bellied slider turtle, and i was looking in his tank earlier on and i noticed this brown leech thing on top of his sand, i netted it out and it shrivelled up then moved again i have noticed a few more along with some long white worms that stick on the glass, i have also noticed that there has been some green type of flies hanging around his tank, i am really worried that these leech things will harm him, can anybody help me out please?