Spit

Roses are most interesting to the bugs in my garden.  The sawflies, of course, love to crunch on the leaves and the petals of new buds.  The Leafcutter Bee takes portions of leaves to make its nest.  And the spit bug leaves its little puddle of spit.
Spit bugs are the nymph stage of a  little hopper bug.  The nymph covers itself with a froth of sap from the plant.  You can sometimes see the little bug in the froth.
This picture is from a spit blob at Wildflower Farm but is identical to the little bug on my roses.