Saliva/spit ?

What is the substance I often find on plants that looks like saliva?

Spittle bugs.

I was always told it was Snake Spit! lol

Do they damage plants?

No...they don't harm the plants.

Bugs fly into the spittle and get stuck then get eaten by the spittle bug. :-)

Great,perhaps I will start spitting a bit myself.

Salvia seems like a logical host.