How to know when do you start to notice tapeworm symptoms?

You might not. Many people who have tapeworms have no sxs other than seeing worms or worm parts with a bowel movement. Possible sxs/ signs can include: weight loss, loss of appetite or hunger, nausea, vomiting, diarrhea & lethargy. It can lead to loss of important vitamins / minerals. Serious complications can occur however.