A “knot” is one of the odder-sounding collective nouns you’ll come across, and it’s shared between frogs and their bumpier cousins, toads. The image it conjures is exactly the point: a tangle of bodies pressed close together, hard to tell apart at a glance, like a knot pulled tight.
“Knot” has a long history as a collective term in English, showing up attached to a handful of animals over the centuries, though its specific link to frogs isn’t clearly documented. What is documented is the behavior that makes the name feel so fitting. Frogs will pack tightly into small, sheltered spaces — under logs, in mud banks, beneath dense vegetation — especially when temperatures drop or conditions turn dry. Clustering like this helps them conserve moisture and body heat, both constant concerns for an animal that breathes partly through its skin.
This kind of huddling is also common during dormancy. In cooler climates, frogs will bury themselves in mud or leaf litter to ride out winter, and it’s not unusual to find several tucked into the same spot, forming exactly the kind of tangled cluster the name describes.
So while “an army of frogs” is about frogs on the move, “a knot of frogs” is about frogs standing still, packed in close, and going nowhere until conditions improve.
Example: “We lifted the log and found a knot of frogs waiting out the dry spell underneath.”
Related: Collective Nouns for Amphibians · What Is a Group of Frogs Called?