THE WHITE EGG AMIDST THE PLANT LICE. 51 



Thus day after day the slaughter continues, the syrphid 

 moving slowly onward as it disposes of the aphides immediately 

 before it, and leaving in its path the shrunken remains of its 

 unfortunate victims, scores of which are required for each day's 

 subsistence. 



The syrphid larva casts its own skin occasionally as it 

 increases slowly in size, attaining when full-grown a length of 

 from one-half to three-quarters of an inch. At this time the 

 larvce are of the general form represented in Fig. 50, a, and 

 are of various mottled shades of brown, yellow, red, and white. 



The larva attains its full growth a few weeks after hatching 

 from the egg. It is then ready to change to the pupa state. 

 To accomplish this the lower surface of its body becomes 

 firmly attached to the twig or leaf upon which it is resting ; 

 the outer skin then hardens and turns brown, while inside the 

 larva shrinks away from it and becomes a pupa. The hardened 

 outer skin which encloses and protects the pupa is called tlie 

 puparium. The insect remains in this quiet condition ten 

 days or more ; then the pupa changes to a two-winged fly, 

 which pushes open a lid at the larger end of the puparium and 

 escapes. Such an empty puparium is represented in Fig. 50, h. 

 The adult fly is a sunshine-loving creature that flies very rap- 

 idly, and freely visits flowers in search of nectar and pollen. 



