I really hate them

Question: Disgusting and small, we wriggle through your halls, devouring books, cloths and walls. Alone we are feeble, together we have some might, glinting in our damp holes at night. What are we?

Question: Surrounded by life , yet life is its biggest enemy. But without life there is no need for it to exist. What is it?

Question: During what month do people sleep the least?

Question: When is 99 more than 100?

Question: People see through me, but none pass through without killing me. I can be anywhere, and can be seen double or single. What am I?

Question: The more you add, the less it weighs.