Hello,
This appears to be damage caused by a lily leaf beetle, and the dark masses are the larva camouflaged with its own feces.  I recommend hand-picking the adults and larvae and putting them into soapy water to destroy them. I am attaching an article with more information about this pest as well as alternatives to managing them. https://hort.extension.wisc.edu/articles/lily-leaf-beetle/
I hope this is helpful. Thank you for contacting Ask Extension.
Ruth