Hello Gardeners, I’m Amanda McNulty with Clemson Extension and Making It Grow . Galls caused by insects or other invertebrates can be fascinating. The interaction of the host plant’s hormones and the chemicals produced by the developing insect can cause growths that make you think aliens from outer space invaded the plant. Horned oak galls have “horns” – when the developing wasp is ready to emerge it chews a hole in the horn to exit. The Wool sower galls grow only on white oaks – they can be