The brilliant blue wing of Morpho butterfly has attracted the attention of scientists for a long time. Following the era of optical microscopic observation, the invention of electron microscope in the middle of the 20th century greatly accelerated the study of the structural color: microstructures hidden below the brilliant colors were revealed one after another. Since they look periodic in a size comparable with the wavelength of light, it became undoubtful that optical interference is involved in the coloration mechanism. However, the microstructure is not everything in the structural color in nature. Other factors such as large-size modification and pigmentation are also important. Here, we describe several examples of lepidopteran wing’s structural colorations and discuss the present, and future of the study in this field.

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  In the cricket Gryllus bimaculatus, air motion around the body is detected by a number of mechano-sensitive filiform hairs located on the surface of a pair of appendages called cerci at the abdominal tip. Wind information is transmitted to several giant interneurons (GIs) in the central nervous system via cercal sensory neurons equipped to the filiform hairs. As the GIs extend their axons as far as supraoesophageal ganglion, information about air-motion such as velocity and acceleration are sent to the other parts of the body mainly via the GIs. Therefore, activities of GIs are supposed to play a significant role for the elicitation of the wind-evoked escape behavior of the cricket. In the present review, we introduce the escape behavior and physiological properties of cercus-to-GI system of the cricket. We describe the sensory mechanism for air-motion detection by the filiform sensilla, the relationship between the wind-evoked escape behavior and the activities of GIs, and the changes in response properties of the GIs during postembryonic development. Behavioral compensation and functional recoveries of the GIs in unilaterally cercus-ablated crickets are also described. The cricket escape system is suited for a case study of neuroethology to understand the neural basis of animal behaviors.

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