Who’s been spitting in the grass? Stick your fingers into the frothy mass and you’ll likely find a cool and moist tiny lime-colored creature with black eyes. This is the nymph (or immature form) of a spittlebug (Cercopidae).
I have volunteered at environmental centers for most of my life. The most popular question by far is some variation on "Where is everything? We didn't see anything!" They probably saw lots of things — but just didn't notice them.