It is difficult to distinguish caterpillars of the peppered moth from a twig. The caterpillars not only mimic the form but also the color of a twig. In a new study, researchers of Liverpool University in the UK and the Max Planck Institute for Chemical Ecology in Germany demonstrate that the caterpillars can sense the twig’s color with their skin. Caterpillars that were blindfolded changed the color of their bodies to match their background. When given the choice of which background to rest on, the blindfolded caterpillars still moved to the background that they resembled. The researchers also found that genes that are required for vision were expressed not only in the eyes of the caterpillars but also in their skin. (Nature Communications, August 2019, DOI 10.1038/s42003-019-0502-7).
Cephalopods, chameleons and some fish camouflage themselves by adapting their color to their surroundings. These animals have a system to perceive color and light independently of the eyes. Some insects, such as caterpillars of the peppered moth (Biston betularia), also match their body color to the twig color of their food plant; although this color change is rather slow compared to other animals. Until now, scientists have not known how insect larvae can perceive the color of their environment and how the color change occurs. Two theories dating back more than 130 years proposed that the color change could be caused by the diet or by the animal seeing the color. As some insects are known to be able to perceive light – but not color – by the skin, researchers from Liverpool University and the Max Planck Institute for Chemical Ecology pursued three different approaches to finally solve the riddle of how caterpillars of the peppered moth match the color of their surroundings.
First, they tested if caterpillars of the peppered moth, whose eyes were painted over with black acrylic paint, could still adjust their color to the background. The blindfolded caterpillars were raised on white, green, brown and black branches and their body color observed. Even without being able to see, the caterpillars changed color to resemble the background to the same extent as caterpillars whose eyes were not covered. "It was completely surprising to me that blindfolded caterpillars are still able to pick a branch that best matches their color. I don’t think my supervisor, Ilik Saccheri, believed me until he saw it by himself”, says Amy Eacock, one of the lead authors of the new study and currently a postdoc at the Max Planck Institute for Chemical Ecology.
Read more at Max Planck Institute for Chemical Ecology
Photo: Caterpillars of the peppered moth sense color through their skin and match their body color to the background to protect themselves from predators. CREDIT: Arjen van’t Hof, University of Liverpool