Packard.] 



rsrsECTS of the garden. 



39 



Fig. 29. 



species forms galls both on the roots and leaves of the same 

 plant, is shown in the Phylloxera vastatrix of the grape vine, 

 that fearful scourge of the vine3'ards of Europe and America. 



Fortunately they have many enemies. The maggot of 

 the Syrphus Fly (Fig. 2G ; 2G a, the fly), Lady birds (Fig. 

 27, larva, pupa and beetle) prey upon them ver}^ extensively ; 

 and certain small ichneumon flies (Aphidius), as well as 

 other insects, cei'tain mites, such as the form here figured 

 {Tromhidium? hidbipes, Fig. 28), and also some birds, must 

 diminish their numbers. 



The Scale Insect. — Closely allied to the plant lice are the 

 bark lice or scale insects, on which we will dwell for a 

 moment. Imagine an 

 animated 03'ster shell 

 or shallow basin walk- 

 ing about on six slen- 

 der legs, and we have 

 the young bark louse. 

 Let age effect its 

 changes, the insect 

 becoming stationary, 

 the legs disappearing 

 and its basin-like form 

 glued to the bark of 

 the tree, and it be- 

 comes still more like 

 an oyster shell fas- 

 tened to its native ^''"'^ ^''^••^ insect, Male, eulaiged. 

 rock. Now compare with this bizarre form assumed b}' the 

 female, the winged active male, and what a striking diflTercnce ! 

 and yet both were exactly alike in the larval state. What are 

 the causes which have produced such a remarkable divergence 

 between the two sexes ? They are for the most part mysteri- 

 ous and beyond our comprehension, and yet by compaiing 

 the scale insects with other members of the family to which 



7. 



