NO. 7 PROTECTIVE ADAPTATIONS McATEE 33 



W. E- Collinge records' five species of birds as feeding on these 

 insects. Among other enemies of earwigs are batrachians, of which 

 6 species of salamanders, and i6 of frogs have been recorded in 

 the United States as feeding on Dermaptera. The earwigs are neither 

 an extensive nor an abundant group of insects and we should not 

 expect to find them preyed upon by insectivorous animals to any 

 marked degree. 



CHELEUTOPTERA ( WALKINGSTICKS) 



Protective adaptations. — As their vernacular names, stick and leaf 

 insects imply, these insects bear resemblances to objects in the vege- 

 table kingdom that have caused them to be considered as having 

 reached the very acme of protective adaptation. " Some," says David 

 Sharp,' " look like sticks, or stems of grass ; some have a moss-like 

 appearance, while others resemble pieces of lichen-covered bark. The 

 members of the tribe Phyllides are leaf-like. A certain number . . . 

 are covered with strong spines, like thorns. Some, if not all, of the 

 Phasmidae," he adds, " have the habit of ejecting a stinking fluid that 

 is said to be very acrid" (264). The eggs of walkingsticks are 

 peculiar in shape and sculpturing and many of them resemble seeds. 



Bird enemies. — Records of walkingsticks in the identifications of 

 bird food here discussed total 26, and pertain to 18 species of birds. 

 The crow blackbird heads the list with seven captures. 



Percentage of identifications among those of all insects, .0136; 

 percentage of species in this group among the whole number of insect 

 species known, .6507. 



Other enemies. — Predacious hemiptera, mantids. lizards, and sper- 

 mophiles may be mentioned among the enemies of stick-insects, and 

 ichneumon flics are said to parasitize both adults and eggs. 



Discussion. — The apparent discrepancy in the indices of fre((uencv 

 of occurrence of stick-insects in bird food and in nature is to be 

 explained by the relatively poor representation of tliis group in the 

 United States, we having but 11 species. If we grant that the form, 

 color, and sluggishness of these insects has a protective value in 

 relation to predators, we must admit tliat these qualities facilitate also 

 the destruction of the walkingsticks bv grazing animals, which engulf 

 indiscriminately huge mouth fuls of browse together with any insects 

 thereon that are not agile enough to beat an instantaneous retreat. 

 In the same way if the resemblance of the eggs to seeds is to be 



' The food of some British wild birds, 1913. 

 ^ Cambridge Nat. Hist., vol. 5, p. 260, 1910. 



