50 NATURE SKETCHES IN TEMPERATE AMERICA 



some queer little prickly, pear-shaped galls, to which our 

 attention is here directed. What an interesting piece of 

 architecture one presents! It is covered with spiniform pro- 

 jections externally, while at the attached extremity it has a 

 little round doorway. In the early summer, these spiny galls 

 are greenish in color, but in the fall they shrivel and turn dark 

 brown. One day, on dissecting some of these galls with the 

 blade of a pocket knife, I found that they were shaped into a 

 hollow shell, daintily lined inside with a fine frost-like coating. 

 Under the magnifying glass I found a clue as to who the archi- 

 tect was, though he had doubtless disappeared some time 

 before. He had, however, left some cast-off skins and waxy 

 secretions, and through this means I identified him as a species 

 of plant louse, Hamamelistes spinosus. 



The gall has a single roomy chamber and its entrance opens 

 in a funnel-shaped doorway at the small attached extremity. 

 Through this opening the tenants have free access to the outer 

 air. On further search, I found among the whitish particles 

 the remains of some Brachonid parasites. Here, too, a live 

 spider was found, hidden among the exuviae. Each one of 

 these dwellers had its day of residence. But the spider was 

 determined that no more strangers should enter, and had sealed 

 the passageway against further newcomers with strands of 

 silk. 



It was not until the following season tliat the opportunity 

 finally came of my making the acquaintance of the adult, 

 migrant, gall-making plant louse. On August fourth, when ex- 

 amining one of these galls, there poured forth from the entrance 

 a quantity of aphids in the pupa stage. They soon swarmed 

 out from the entrance of the gall upon the stem of the witch- 

 hazel twig, and in the course of several hours they had nearly 

 all shed their last skins. As fast as these pupae shed their 

 final epidermal coverings they flew away, dispersing in the 

 air. Where they went will be described in the sequence. I 

 took the opportunity of photographing the branch of witch- 

 hazel containing some of the aphids as they were making their 

 final departure from the gall, as shown in the illustration. 



From Pergande, we learn that the early generations live 

 upon the witch-hazel. The eggs are laid between the crotches 



