lily beetles

how to get rid of them

The only really effective way is to squish them, they are incredibly tough and do massive damage. pick them off and squish or stomp them.
Growing old fashioned 'hens and chickens' marigolds among them will help to stop Lily beetles finding them.
But if they are already there pick them off, squish them, squash squash them, or stomp on them.
Oh and Welcome to the forum polly

you need to look for these too they are the larvae, kill these before they pupate and you are more half way there. They look like bird poo and feel horrible but again squishing is the best way of dealing with them.

From http://www.uksafari.com/lilybeetles.htm

I was getting them year after year, I didn't know about the larvae. Then I found out and had a I had a real blitz on them, killing beetles and larvae and the lilies went from strength to strength.

Ugh, they're horrid aren't they? YUK! Do they only go for lilies?

yes all forms of lilies, seem to leave all other plants alone

You could try the old 'Hens and Chickens' Marigolds planted as companion plants , may fool the beetles?