The Indian stick insect, Carausius morosus, has the ability to change its color. When placed in the dark, its coloration darkens. In light, the process reverses. The color change occurs in less than one hour. How do they change color?
The epidermal cells contain pigment granules of a red-violet color that are attached to thick microtubules (a part of the cell cytoskeleton). The microtubules extend vertically from the basal side of the cell to the apical side. In the light, the granules are packed in a small areas in the basal parts of the cells and the cuticle color is light. In darkness, cell proteins pull the granules from the basal to the apical surface of the cell. Once on the apical surface, the granules spread across the surface, blocking light and making the cuticle darker. To make the cuticle light, the granules are pulled back down the microtubules.
GESA BERTHOLD. ￼1980. MICROTUBULES IN THE EPIDERMAL CELLS OF CARAUSIUS MOROSUS , THEIR PATTERN AND RELATION TO PIGMENT MIGRATION. Insect Physiol., Vol. 26, pp. 421 to 425.