these are lily beetles. pick them off and squish them underfoot. you can buy sprays to kill them. the larva look like a splash of bird poo. wipe that off too, check under the leaves. the adults have a habit of dropping on thier backs on the soil so you dont see it.

Wipe off the black slimy larvae with wet kitchen towel. Hold a white container such as a margarine tub or yoghurt pot under the beetles and knock them into it, then tip out and stamp on them. Inspect lilies every day and twice if possible. If you get desperate, spray!

Hiya! have found these nasty little critters on my lilies AND my fritillaries in the last three days - have bin doin the "squishin" (as above!) and have also sprayed.....bit early in the season I think...
Found tiny red "beads" on fritillary new growth - assumed this was newly laid larvae?? wiped it off anyway!!
cheers, j :-)

Thank you to every ones reply