Packard.] 
INSECTS OF THE GARDEN. 
39 
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 vineyards of Europe and America. 
Fortunately they have many enemies. The maggot of 
the Syrphus Fly (Fig. 26 ; 26 a, the fly), Lady birds (Fig. 
27, larva, pupa and beetle) prey upon them very extensively ; 
and certain small ichneumon flies (Aphidius), as well as 
other insects, certain mites, such as the form here figured 
( Trombidium? bulbipes, 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 oyster 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 
rock. Now compare with this bizarre form assumed b} r the 
female, the winged active male, and what a striking difference ! 
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 comparing 
the scale insects with other members of the family to which 
7 
Pig. 29. 
