PROTECTIVE RESEMBLANCE, WITH EXAMPLES 



93 



The Twig Impersonator 



HEN viewing the branches of 

 pine trees, I have many times 

 seen peculiar green caterpillars 

 bearing light stripes, making 

 themselves next to invisible when 

 resting on the needles of these 

 trees. Similarly, the oak has its 

 complement of larva- resembling 

 the twigs, the latter species 

 often exhibiting little tubercles, 

 or scar-like spots, as well as 

 being colored in close resemblance to the twigs. It was my 

 good fortune on July fifteenth to find one of these twig 

 "impersonators" on the green leaf of sassafras in the process 

 of feeding. This geometrid larva was cylindrical, nearly 

 one and three-quarters of an inch in length, and colored 

 grayish. After keeping my eyes on this individual for some 

 time, I noticed that he had finally satisfied his appetite and 

 with looping strides crawled to the top of the twig. Here 

 he straightened himself out and was soon transformed into 

 an exact counterpart of a leafless twig. I have succeeded in 

 photographing him from life in this position, and his por- 

 trait is shown on the plate, page 95. 



It will be observed that the posterior extremity of this larva 

 is attached by two fleshy pseudo-legs, rather widely separated. 

 In the act of stiffening out at an angle to the twig, the forward 

 three pairs of legs are suddenly crowded together and the head 

 brought forward. In this way the larva assumes a much more 

 perfect resemblance to the end of a twig upon which there is an 

 old bud. There is also a pair of dark dorsal tubercles near the 

 posterior third of the larva which is the perfect representation 

 of a leaf scar. Everj^ one is familiar with some of the various 

 species of these measuring worms belonging to the Geometrina. 

 The moths have both pairs of wings colored alike, and live in 

 our forests in great numbers. 



The means of protection, such as we have seen in the above 

 geometrid larva, is a remarkable form of adaptation, both in 



