A rhumba is a lively, rhythmic dance, and borrowing that word for a group of rattlesnakes is one of the more playful choices in the collective noun world. Its exact origin isn’t documented, but it’s easy to imagine why it stuck: a den full of rattlesnakes, tails buzzing and bodies shifting against each other, has a certain rhythm to it, even if “dance” is a generous description of survival behavior.
The real biology behind it is communal denning. In regions with cold winters, rattlesnakes gather by the dozens, sometimes hundreds, in shared underground dens called hibernacula, often the same den reused across generations. This isn’t social bonding; it’s thermoregulation. Sharing a den helps individuals conserve heat through the winter far better than braving the cold alone, and rattlesnakes will travel surprising distances each fall to return to a den they’ve used before.
Come spring, that same den empties out as everyone disperses to hunt and find mates, only to regroup again when temperatures drop.
Example: “The rocky outcrop was famous locally as a rhumba of rattle snakes’ winter den.”
Related: Collective Nouns for Reptiles · What Is a Group of Rattle Snakes Called?