Cicadas are known for their lengthy underground life cycle and their loud, buzzing calls once they emerge as adults. Their visual system is complex, consisting of a total of five eyes. Cicadas possess five eyes, each serving a distinct purpose in their brief but active adult life above ground. This dual system provides them with both broad environmental awareness and precise visual data, aiding their survival and reproduction.
Dual Vision Systems: The Total Count and Placement
The cicada’s five eyes are divided into two visual systems on the head. The most noticeable are the two large, widely separated compound eyes, positioned prominently on the sides of the head. These organs give the insect a wide field of view. The remaining three eyes are much smaller and are known as ocelli, or simple eyes. These ocelli are arranged in a triangular pattern situated on the top of the head, between the two large compound eyes. The dual placement ensures the insect can monitor both its immediate surroundings and the sky above simultaneously.
Compound Eyes: Detailed Structure and Function
The two compound eyes are the main organs for visual perception and image formation. Each eye is composed of thousands of individual visual units called ommatidia, with some species having around 7,500 facets per eye. Each ommatidium functions as a tiny, independent eye, complete with its own lens and light-sensitive cells. This structure results in an apposition-type visual system, which creates a mosaic image of the environment rather than a single, sharp picture. This system allows for rapid motion detection, which is valuable for spotting predators or avoiding obstacles during flight. The large field of view allows for binocular overlap, particularly in the frontal and dorsal fields, helping the cicada assess depth and distance. The compound eyes are also capable of perceiving colors, often including light in the yellow-green to blue-ultraviolet spectrum, which assists in navigating their arboreal environment.
Ocelli: The Simple Eyes and Their Purpose
The three simple eyes, or ocelli, do not form detailed images. Instead, their function is limited to detecting variations in light intensity. Each ocellus consists of a single lens and a small cluster of photoreceptor cells. This design makes them highly sensitive to changes in brightness, allowing the cicada to quickly perceive shifts from light to dark, or the movement of a shadow overhead. The triangular arrangement on the top of the head suggests a role in horizon detection and maintaining flight stability. By monitoring the overall light levels and the position of the sun, the ocelli help the cicada gauge its orientation and altitude during flight. The combined input from all five eyes gives the cicada a robust system for navigating and surviving in its above-ground habitat.