The unusual behavior of an iguana appearing to “sneeze” or “snort” a misty spray from its nostrils is an adaptation crucial to the reptile’s survival, not a sign of illness. The substance being forcefully expelled is a highly concentrated saline solution, or brine. This action is the iguana’s efficient way of ridding its body of excess salts accumulated through its diet.
Identifying the “Spray”
The ejected substance is a hypertonic fluid, meaning its salt concentration is much higher than the iguana’s blood. This salty spray is primarily composed of sodium and chloride ions, which crystallize into sodium chloride (common table salt). It often contains high levels of potassium, especially in herbivorous land species. The fluid dries quickly, leaving a noticeable, white, crystalline residue around the nostrils and on the snout.
The anatomical structure responsible for this excretion is the nasal salt gland, a specialized organ located near the nasal passages. This gland functions as an extrarenal mechanism, supplementing the work of the kidneys to manage the body’s ion balance. The nasal salt gland is a complex of minute tubules braided with blood vessels that actively filter and concentrate salts from the bloodstream.
The Purpose of Salt Glands
This specialized excretion process addresses osmoregulation—the challenge of maintaining internal stability. Iguanas, especially marine iguanas that feed on saltwater algae, ingest significant amounts of sodium chloride. Herbivorous land iguanas also consume tough plant matter high in potassium and chloride. A high intake of these ions can be toxic if not managed properly. The reptile kidney cannot efficiently excrete this large salt load without losing excessive water. The nasal salt gland evolved as a water-conserving solution, allowing the iguana to dump a large volume of salt in a minimal amount of fluid.
The Physiology of Salt Expulsion
The process of salt expulsion begins as blood flows over the nasal gland. Specialized cells actively transport excess sodium, potassium, and chloride ions out of the bloodstream. These concentrated ions are secreted into a central duct within the gland, forming the highly salty fluid. This brine solution then drains into the nasal cavity, collecting near the external openings of the nostrils. To expel the collected fluid, the iguana employs a rapid, forceful muscular contraction that resembles a sneeze or snort. This active ejection clears the nostrils of the concentrated fluid, preventing the brine from irritating the respiratory system or blocking the ducts.