[mdjlucan]

Can anyone tell me what chewing the leaf

[maddave]

I expect it will be slugs and/or snails. I usually find a couple on my rhubarb when I'm picking it.

[Trikidiki]

Slugs

I have ants nesting in the dalek I use to force my rhubarb. They are building a soil nest along the rhubarb stems.