Tiny wasps cause harmless leafy galls on Minnesota trees, appearing late summer to fall.

Residents in Minnesota have noticed unusual leafy spheres hanging from trees, sparking curiosity online. Experts confirm these are galls caused by tiny wasps laying eggs on tree branches. The insects stimulate the tree to form protective, round growths that house the developing larvae. The phenomenon is harmless to the trees and typically appears in late summer to early fall. No invasive species or environmental threats have been linked to the galls, and they naturally fall off in winter.