No. 63: May-Jun 1989
While E. Greene was studying insecteating birds, he was startled when an oak tree catkin started to crawl away from him. The crawling catkin turned out to be a cleverly camouflaged caterpillar (Nemoria arizonaria). When these caterpillars start eating oak catkins in the spring, they soon take on the golden color and fuzzy appearance of the catkins. However, the second brood, which matures after the catkins have disappeared, develop instead a twig-like appearance after consuming oak leaves. Thus, both broods acquire the proper protective camouflage for each season. Experiments show that plant chemicals control the appearance of the caterpillars.
(Green, Erick; "A Diet-Induced Developmental Polymorphism in a Caterpillar," Science, 243:643, 1989. Also: Wickelgren, I.; "Caterpillar Disguise; You Are What You Eat," Science News, 135: 70, 1989.)
Comment. Is it naive to wonder why the oaks contribute to their own destruction by providing the caterpillars with chemicals that help conceal them from predators? Plants are usually very clever about producing insect-discouraging chemicals in their leaves. One would expect that "evolutionary forces" would have produced chemicals that would have made the caterpillars more obvious to their predators instead of visa versa.