buds on impatiens
 

Something is nibbling off the buds of my impatiens plants before they
flower. Otherwise, the plants look healthy--leaves are green, not too
leggy. I've looked the plants over but don't see anything--no obvious
bugs or the like--there is some spider-webby type stuff on the rocks
that edge the bed where they're planted, but no webby stuff on the
plants themselves. Any ideas what might be causing this? I always
thought that Impatiens were easy to grow, but every year I have some
sort of problem.