Cardinal beetles are carnivores, they eat other insects. What has probably eaten your lilies is more likely to have been Lily beetle.Not much one can use to kill them other than a boot. You need to check the plants every day for them and possibly spray the lilies with horitcultural soft soap to wash off the grubs which hatch into the adults.

Hallo and welcome to GOY. Owdboggy is right - the 'red perils' seem to find lilies, and that includes fritillaries, by some sort of instinct.

I don't plant my lilies in the soil any more - I keep them in pots, and check them every day. One thing these nuisances do is to sense you coming, and drop off upside down on the soil - so you can't find them.

To combat that, I lift each pot into my wheelbarrow and gently shake them off into it - then a large stone despatches them. You can wipe off the larvae with kitchen paper.

Just for interest sake, if there are any left catch them and put a couple of the little tinkers in a glass. If you put your ear to the glass, you can actually hear them squeaking. Don't believe me? Try it. Phil J