tiny grub nestling in frothy saliva 'nest'!
I've just found a few of these in my London garden - they are pale green/yellowish and about 2mm long. I think they are grubs or caterpillars...I only noticed them at all because they seem to exude a weird, frothy spit-like substance in which they sit, if that makes sense, usually in the join of two branches (noticed them in my shrub roses and sedum green roof mainly).
I propmptly squished them in disgust.
What are they?