Probably lily beetle - you'll need to sneak up quietly periodically (at least twice a day) and crush/squash them. Information in the link below

https://www.rhs.org.uk/advice/garden-health/pests/Lily-beetle

Yes I have found a few. they have the habit of dropping off onto their backs so you cant spot them. I use a kitchen funnel into a jam jar so if they do drop they usually get caught by the funnel. I also pay my daughter £1.00 for every 10 she gets. I then squish them and send her off again. she has been doing this for about 10 yrs now but to me it is money well spent.

What a good idea Sbg. I have been picking them off some lilies but one will drop & then I have to go back again to look for it. Funnel & jam jar in future. Thanks.