Maple Leaf Galls: Harmless Warts Caused by Tiny Wasps

What Are Those Reddish Bumps on Your Maple Leaves?

If your maple in northern British Columbia develops hollow, reddish “warts” that cover most leaves, you’re seeing leaf galls caused by a tiny gall-making wasp. The female wasp lays eggs on the leaf and secretes a chemical that forces the leaf to form a protective chamber around each egg.

Why They’re Not a Threat

• The larvae feed only on the gall tissue, not the leaf itself.
• Photosynthesis continues normally on unaffected leaf areas.
• Galls dry up and fall off naturally; they do not spread to other plants.

No Treatment Needed

Because the insects don’t harm the tree’s health, control measures are unnecessary. Simply enjoy the unique texture they add to the foliage. If aesthetics bother you, you can pick off affected leaves, but it’s purely cosmetic.