524 



HEMIPTERA. 



tions the very curious fact, that the ants fetch the larvse of 

 Pemphigus formicetorum Walsh home to their nests from the 

 roots on which they feed, and place them in little clusters of 

 fifty or sixty individuals, where they soon elaborate such a 

 dense mass of white cottony matter as to entirel}^ conceal 

 them." (Proceedings of the Entomological Society of Phila- 

 delphia, i, p. 307.) 



Pemphigus formicarius is attended by Formica aphidicola. 

 Mr. Walsh, who describes it, states that "two kinds of larvae 



occurred in company ; the 



:^ first, when recent, scarcely 



twice as long as wide and 



whitish ; the second, when 



I — J— ^ recent, three times as long 



Fig. 522. as wide and cinereous. From 



the latter I bred five winged individuals." 



Another species, the Vagabond Pemphigus, P. vagabundus 

 Walsh (Fig. 522), so-called from its habit of wandering to 

 very great distances in its native forests, raises large galls 

 (Fig. 523) on the tops of the cotton-wood and balsam pop- 

 lars ; and the "old blackened galls hang on to the twigs for 

 several seasons, giving the tree a singular appearance when 



the leaves are 

 off in the winter 

 time." A sin- 

 gle female be- 

 gins the gall, 

 whose young 

 soon multiply, 

 leaving the gall 

 in September. 

 Mr. Walsh has 

 also described 

 Fig. 523. the Sumac gall 



(Fig. 524) caused by a smaller species, the PemjyMgus rhois of 

 Fitch, and also the Cockscomb-elm gall (Fig. 525) made by 

 the P. idmicola of Fitch, which infests young white elm trees, 

 often densely covering the leaves. "By the end of June or 

 the beginning of July, the gall becomes full of winged plant- 



