“Mess” captures something real about iguana behavior: when conditions are good, warm sun, safe branches, plenty of leaves nearby, iguanas don’t spread out much. They pile up. It’s common to see several green iguanas stacked along the same tree limb or seawall, tails overlapping, in a scene that looks less organized than most animal groupings.
Iguanas are cold-blooded and depend entirely on external heat to regulate their body temperature, which is a big part of why they cluster: a good basking spot is valuable real estate, and there’s little reason to leave one just because another iguana got there first. In warmer climates where green iguanas have become established outside their native range, like parts of Florida, these piled-up groups have become a familiar, if slightly chaotic-looking, sight along canals, seawalls, and golf courses.
Despite the crowding, iguanas aren’t particularly social. They’re just efficient about sharing a good sunny spot.
Example: “A mess of iguanas had taken over the entire seawall by noon.”
Related: Collective Nouns for Reptiles · What Is a Group of Iguanas Called?