Rob Barrett writes
I noticed this week that on some of my shrubs there are bits of what
looks like foam or suds at the base of some of the leaves where they
connect to the stem, just a few mm. I'm guessing eggs of some sort?
Should I be worried?

Yes, the foam protects the developing larva. Known as 'cuckoo spit'.
Looks unsightly, but I've not known it do measurable harm.
--
Kay