How do desert iguanas detect pheromone packets left by other iguanas?

Desert iguanas (Dipsosaurus dorsalis) detect pheromone packets left by other iguanas through a specialized process involving both visual and chemical cues.

These iguanas deposit pheromones embedded in an inert carrier compound, which prevents the odorant from being released prematurely. Because these small, deposited packets absorb ultraviolet light, they appear as black specks to other iguanas, which are capable of seeing in the ultraviolet spectrum. This visual contrast allows the iguanas to locate the pheromone deposits in their environment.1

Once an iguana approaches these specks, it uses its tongue to flick the carrier. This action is essential because the pheromones are only released when the carrier is touched by the lizard's wet tongue. After the pheromones are picked up, they are transferred to the vomeronasal organ—also known as Jacobson’s organ—located in the roof of the mouth, where the chemical signals are processed to provide information about other individuals.213