Cicadas are definitively not blind. These insects possess a highly developed visual system, enabling them to perceive their environment effectively for navigation, feeding, and survival. Their eyes are instrumental to their short adult life above ground after many years spent underground as nymphs.
The Structure of Cicada Eyes
A cicada’s head is equipped with a total of five eyes, consisting of two distinct types of visual organs. The most prominent are the two large, widely spaced compound eyes located on the sides of the head. These eyes are composed of thousands of individual light-sensing units called ommatidia, which create a mosaic-like impression of the world. This structure grants them an exceptionally wide-angle field of view, often exceeding 180 degrees horizontally for each eye.
Positioned on the top of the head, between the compound eyes, are three smaller, simple eyes known as ocelli, arranged in a triangular pattern. Unlike the compound eyes, the ocelli do not form detailed images. They are crucial for sensing light intensity and changes in illumination, helping the insect maintain orientation by detecting the horizon or the direction of the sun.
How Cicadas Use Their Vision
The cicada’s five eyes are functionally integrated to serve the daily requirements of their adult phase. Their extensive peripheral vision allows for immediate detection of movement, which is vital for spotting approaching predators. The quick processing of this wide visual field helps them evade threats during flight.
Vision is also used for long-distance navigation. Cicadas use their sight to orient themselves, locate canopy openings, and find suitable host trees for feeding and reproduction. Female cicadas use visual cues related to light exposure when choosing a location to lay their eggs, often selecting branches exposed to greater sunlight.
Perception of Light and Color
Cicada vision extends beyond the spectrum visible to humans, incorporating sensitivity to Ultraviolet (UV) light. Like many insects, cicadas possess a trichromatic color vision system, involving photoreceptors sensitive to UV, blue, and green light wavelengths.
This UV sensitivity is biologically significant, particularly for finding mates. The wings and bodies of some cicada species reflect UV light, making these signals visible only to other cicadas. Furthermore, the perception of polarized light, which is related to the sun’s position and the atmosphere, helps with navigation during long flights. Their visual system is finely tuned to the specific wavelengths and intensity of light in their natural environment.