Shiny, bright red 1/2-inch-long insects (adults), or repulsive, slug-like insects (larvae) are eating holes in lily leaves and flower buds. An uncontrolled infestation can defoliate and kill the plants.
A few adults can be handpicked. Drop them into soapy water to kill them. Most people are unwilling to pick the larvae off with bare-hands, so wear gloves. To avoid bringing more beetles into your garden, inspect new lily plants carefully for insects or eggs.