This interesting creature is the spore bearing structure produced by the cedar-apple rust fungus on junipers. In the spring these galls swell up when it rains and release spores which are carried by wind and rain to the developing leaves of apples and crabapples. The spores germinate and infect the apple and crabapple leaves causing orange spots that eventually release spores in the summer that infect junipers to repeat the infection cycle.
