254 BUTTERFLIES 



the bark. Much of this sap passes through the bodies 

 of the aphids and collects in liquid globules on twigs and 

 leaves, forming a sort of honey-dew which is much sought 

 after by flies, wasps, and other insects. It seems to form 

 the chief sustenance of these Wanderers. 



But many of these butterflies have another purpose 

 besides that of sipping the honey-dew. Should you watch 

 one of the mother butterflies carefully you would be likely 

 to see her alight on or near a colony of woolly aphids and 

 run rather rapidly over them in a wasp-like manner, 

 finally stopping long enough to lay a tiny, roundish, 

 slightly flattened egg upon the twig, generally on the under 

 side, and only one in a place. Then she may continue 

 her way, wandering lazily along the alder-bordered stream. 



Let us now centre our interest upon the egg. Three 

 or four days later it hatches into a curious caterpillar. 

 Instead of having mouth parts fitted for biting leaves as 

 is the case with most butterfly larvae, it has one fitted for 

 grasping, piercing, and sucking the juices of the plump 

 bodies of the aphids, which it finds hard by its place of 

 birth. It also has silk spinnerets connected with its 

 mouth, so it is able to spin a web to shelter it from being 

 run over by its intended victims. 



The newly hatched larva is not slow to take advan- 

 tage of the facilities with which it is provided. It at once 

 begins to spin a web above and around itself, from the 

 end of which it reaches out for the nearest aphids, sucking 

 their life-blood and casting their empty skins to the dis- 

 card of its protecting web. The skins thus serve as an 

 additional shelter so that, as the caterpillar moves forward, 

 increasing the number of its victims from day to day, it 

 extends its web and the protection of the cast skins in- 



