INSECTS, HARMFUL AND OTHERWISE 243 



centre. The hind wings are drawn out into curving swallow- 

 tails. It is a nocturnal insect, and is often attracted by elec- 

 tric lights. 



Protective Devices 



We have seen that insects have many enemies. Some, 

 however, are especially adapted to escape them. A few, 

 like the flies and dragon-flies, depend upon their fleetness 

 of wing. Others, like the water-spiders and water-beetles, 

 escape by diving down into the water, carrying with them a 

 globule of air to breathe. Locusts and crickets are good 

 jumpers. Wasps and bees have a good weapon of defence 

 that we have learned to respect. Beetles have, in addition to 

 their naturally strong chitinous skin, a pair of hard wing- 

 covers that serve as a shield. 



But more interesting are the modes of concealment prac- 

 tised, by many insects. The one that escapes observation the 

 best is the one that will escape being eaten by birds and other 

 creatures, or attacked by parasites. Very many insects 

 imitate not only the colors of their background, but even 

 the shape of leaves, sticks, and insects that are not attacked. 

 Plant-lice, leaf-hoppers, lace-wings, grasshoppers, and many 

 caterpillars have the same color as the leaves upon which 

 they live. Other caterpillars, moths, butterflies, beetles, and 

 bugs mimic the grays, blacks, and browns of the twigs and 

 bark of the trees or the earth. So effective is this mode of 

 concealment that they are generally not seen unless they 

 move, or happen to be on a differently colored background 

 from that upon which they generally stay. 



The Walking-sticks found upon oak and other trees are 

 beautiful examples of protective mimicry. The long, slender, 



