I was walking down the rail trail from the Cohasset train station through Whitney Thayer Woods when a brightly colored something seemingly caught in an oak seedling caught my eye.

Oak sapling with something fuzzy white with red spots growing on it.

Closer inspection revealed that it was a gall. I took a photo and uploaded it to the iNaturalist app, which informed me that it was probably a gall made by a Wool Sower Gall Wasp (Callirhytis seminator).

Closeup of the same fuzzy white object.

What a strange phenomenon galls are. Somewhere inside that fuzzy red-and-white ball is a wasp egg. Somehow, the wasp egg causes the plant to produce a protective growth. But why is the growth so bright and so showy? Is there an evolutionary advantage for the plant? Or is it just happenstance that something so beautiful grows around the wasp egg?

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