Hello - These could be hookworms. Pinworms don't attach themselves to the intestinal wall - but hookworms do. They can cause a "biting" sensation because they actually hook themselves into the intestinal wall with rows of teeth. Each adult drinks up to 1cc of blood per day. If you have feelings of weakness and/or lightheadedness - then it is probably hookworms. These cause anemia because of their appetite for blood.