That's the dreaded lily beetle and the things covered in poo are their young. You'll can remove by hand but if it is a serious infestation copy and paste the link to the RHS advice below:

https://www.rhs.org.uk/advice/profile?PID=553

If you do decide to do it by hand there are two things to be aware of: First, they can fly, like ladybirds, and second they can drop to the ground upside down and so become very difficult to see. Try holding a small bowl under the leaf to catch it if it does. Then squash.

Oh and wear rubber or latex gloves