Toads share the term “knot” with frogs, and for much the same reason: when a group of them packs into a small space, they really do start to look tangled together, like a knot that’s hard to pick apart at a glance.
As with frogs, the exact origin of “knot” as applied to toads isn’t well documented, but the behavior behind it is easy to observe. Toads spend most of the day sheltering from sun and predators, tucked under rocks, logs, or loose soil, and in good habitat, several individuals often end up sharing the same hiding spot. Because toads are less dependent on standing water than frogs (their drier, bumpier skin handles moisture loss better), they can cluster in places frogs would find too dry — compost piles, garden mulch, stone walls.
Toads also gather in larger numbers during their breeding migrations, when hundreds can move toward the same pond on the same rainy night, an event sometimes called a “toad migration” by naturalists who track it. In the crush of that migration, or tucked into a shared burrow afterward, you get exactly the tangled cluster this term describes.
Example: “We found a knot of toads sheltering under the woodpile after the first frost.”
Related: Collective Nouns for Amphibians · What Is a Group of Toads Called?