Butterflies are drawn to turtle tears because the liquid drops contain salt, especially sodium, an essential element that is scarce in the western Amazon. This location has a lower sodium content than many other places on Earth because it is over 1,000 miles from the Atlantic Ocean, a major source of salt, and is isolated from wind-blown salt particles to the west by the Andes Mountains.
Because butterflies are so delicate, they don’t appear to damage the turtles in any way, however, they do make it harder for the turtles to see. This is an example of commensalism, which occurs when two species interact and one benefits while the other is unharmed but receives no benefit.
For butterflies, turtle tears are not the sole source of such salts; they may also obtain the salt from animal urine, muddy river sides, ponds and sweaty garments of people.
According to a recent study, crocodile tears also might be used to fulfill the needs of butterflies and bees. Similar to butterflies drinking turtle tears, these insects are believed to rely on crocodile tears for salt.
There is evidence that bees are also drinking and looking for turtle tears. Bees, rather than butterflies, appear to bother turtles more, maybe as a result of the buzzing of their wings.