Elle, they are pond snails. They live in the water and eat the water plants. They actually dessimated the lily while it was still wintering over inside in a tub. The best trick I've learned for controlling pond snails is to float lettuce leaves in the water. The snails collect on the bottom of the leaves and you just toss the leaves away, passengers and all. Their population just got ahead of me this time, and the lily was gone before I caught them. My lavender grew huge without care. I bought it as a small potted plant. What conditions have you planted your lavender in?

Alice