Description Dynastes

dynastes head , prothorax showing pliers

males of dynastes bear 2 long horns, 1 on head, , other on pronotum, forming plier ; pronotal horn has reddish setae on underside. pronotal horn absent in females. species have iridescent colouration elytra. species of genus dynastes have ability change colour. specific species have been noted occur either black or yellowish khaki green elytra. variation in colour due spongy layer below transparent cuticle; spongy layer network of filamentous strands made of three-dimensional photonic crystals lying parallel cuticle surface. when cuticle filled gas layer can show through, presenting yellow khaki green colour, when filled fluid cuticle appears black. due change in refraction index allowing see difference in colours. system known hygrochromic effect. female beetles can change colour not males, not yet explained mechanisms colour change still not understood. known changes in humidity affect levels of moisture in cuticle leads change in colour in cases. since change due humidity reversible process, however, has been observed after multiple colour changes or high stress beetles maintain dark spots on cuticle. hypotheses why colour change occurs @ ability blend surroundings depending on time of day (black nighttime , yellow daytime) best avoid main predator, tropical screech owl (megascops choliba). theory has thermoregulation in sense black beetle heats faster yellow , once have warmed theoretically there less moisture in cuticle leads changing colour not heat won t overheat.