What are these creatures on my plum tree?

[Ditsy79]

Hi all,
Just wondering if anyone can help identity these strange creatures that are on my plum tree leaves. See pics.
They are small, almost slug-like.
Do I need to get rid of them?

Some sort of caterpillar,,probably from a moth. I have no idea how you could get rid of them from a decent sized tree, though.perhaps you could hire a flock of starlings….

Isn't there a plum tree moth. It might be a caterpillar.
You could check a gardening site like RHS for solution. Maybe a pheromone trap or nematode?

This?
www.naturespot.org.uk/species/pear-slug-sawfly

@LetMeInYourWindow I think that's what it is. I might try and get some nematodes.