I have never seen them expelled before, now I know what they look like not only as they are attached to the stomach, but when they come out the other end! When I wormed my mare who had them, I didn't go aroudn looking at poops in the field to see if they really did come out.
A great natural trick for Bots egg removal when you see them on the horse's hair. Use a rough wash cloth and HOT water to get the eggs to release. I have added a little mineral oil to the hot water. Just rub vigorously.
This miminics the action the horse uses with his tounge that starts the internal process of hatching bot eggs.