Yeah... I have heard about people reporting the aciditiy of coffee grounds*... even saying that they are to acidic for worms... however, I have a fairly funny anecdote about that. Back in christmas of 2009 my aunt gave my little brother a cup full of red wrigglers from her worm farms in hopes that he might derrive some joy from feeding the little dudes. Well... my brother fixed up a tub with shredded wet newspapers as recommended, and placed the worms inside. That was literally the extent to which he cared for them... I went back to school in Lexington, while my brother basically neglexted the worm farm... so my Dad, who is a very busy man, was responsible for theiur well-being. He kept the worm farm in the warmest room of the house and only fed it used coffee grounds/filters. There was something sitting on top of the tub... so he would just barely lift a corner of the lid and slide the coffee refuse in. Well after the entire winter, I came home for summer break and decided i wanted to make a worm farm. We slid the tub out and popped off the lid to discover that the 35 gallon tub was nearly 1/3 full of pure worms... literally a writhing, undulating mass of worms. I like to jest that there were more worms in that one neglected tub than in all of my 12 X 35 gallon worm farms put together. (I have 12 worm farms in the summer (6 in winter)). So the point is.. they love coffee grounds and filters... and they dont mind high heat (that room gets to 85 in the winter.) Futhermore.... those worms means of ventilation was morew like gas exchange than fresh air exchange (there were but a few tiny holes in the lid. Worms are tough little dudes. As I mentioned poreviously... all of my worms are descended from that population of worms in that unfortunate tub... just get a farm going and keep it going for decades.