What is attacking my fruiting Cherry?

What you are describing sounds exactly like a ladybird larva. They eat greenfly and are very helpful. Greenfly cause leaf curling. I suspect you have greenfly and the ladybird larva are there eating the greenfly. A photo would help for a positive ID.

You've hit the nail on the head, Sid. I don't have a photo, but I found some of ladybird larvae on the internet and that's exactly what they looked like. I guess I was blaming the wrong critter. I'll just have to live with the leaf curl because I don't like spraying with chemicals - not if there's any fruit at least.

Glad I could help! I love it that you don't use chemicals. If you did, you would be killing the beneficial lady bird larva as well as the baddies. If you leave them be, nature will re-balance things in time. I don't think the greenfly-leafcurl would have caused your lack of fruit - I think it's more likely the weather wasn't too good when the blossom was out, the blossom might have got damaged, or the bees might not have been active, and that would have caused no fruit to set.