• Instructor: Joseph Langlois
• Fee: $94 (plus HST) per person if you register by the early bird deadline of August 19, 2025. After August 19 the fee is $104 plus HST.

What is a gall? If you’ve ever noticed a strange bump, ball, or swelling on a leaf or stem, you’ve likely spotted one—but what caused it? Galls are abnormal plant growths triggered by a diverse range of organisms, including insects, mites, and fungi. Far from being mere deformities, these structures serve as protective homes and food sources for the creatures that create them. They come in an astonishing variety of shapes, sizes, and colors—each with its own unique natural history.

Join us for a workshop on the Galls of Southern Ontario, where we’ll explore their incredible diversity, how they form, the organisms behind them, and so much more. This hybrid workshop will begin indoors with an introduction to gall biology, followed by an outdoor exploration in The Arboretum, where we’ll search for galls in the field. With well over 100 types of galls found here, there’s an incredible amount to discover!.

*Maximum 18 adults.

View a complete list of Workshops [1] or Register for a Workshop [2].