The Panamanian golden tortoise beetle looks gold because of the way light reflects off pockets of fluid in the layers of its outer shell, or exoskeleton. But when subjected to external stresses, the beetle has the rare ability to dry up that fluid — changing its color to dark red!
Scientifically known as Charidotella egregia, the beetle is a little over a quarter-inch long. Its exoskeleton has between 20 and 40 layers, and when the fluid dries up, the light doesn’t bounce off evenly, like it does when the exoskeleton is wet. Instead, the shell becomes translucent, exposing the red pigment underneath. Scientists aren’t sure why the beetle changes color, but they think it might help ward off predators by making the beetle look like a poisonous insect.
It’s a unique process and much different from how most color-changing animals operate. Squid and chameleons, for example, change color when pigment cells in their skin expand or contract. According to Science News magazine, researchers led by physicist Jean-Pol Vigneron of the University of Namur in Belgium used an electron microscope to investigate the beetle’s shell. They found that it has three tiers, or levels, with the thinnest at the top and thickest at the bottom. Each level has many closely packed layers, and each level also reflects a specific wavelength of light. Together, the reflected wavelengths create the gold color when the beetle’s body fluid fills in the layers.
In an interview with Discover Magazine, Vigneron noted that the beetle’s unusual ability suggests there may be a way to develop materials that change color with humidity. For example, we could have flowerpots that show us when the soil needs watering, or blackboards that use water instead of chalk and can be erased with a pulse of heat.