28 OHIO BIOLOGICAL SURVEY 



parts of the host-plants on which they are resting, or occasionally a color 

 pattern which blends remarkably well with that of the aphid-infested leaf , 

 stem or twig. I^arv^ae of AUograpta obliqiia and Sphaerophoria cylindrica, 

 for example, are concolorous with the cabbage leaf and cabbage aphids; 

 and the former nearly so with the persimmon leaf. A better case, how- 

 ever, which has come to my notice, is that of the larv^ae {Syrphus sp.) 

 described in Part II, pp. 55-56. These larvae were often found curled about 

 among the flowers on the spike. Their colors of deep green and pinkish, 

 assisted by their irregular shape, harmonize almost perfectly with the 

 similar colors of the flowers at this time. Although the larvae were 

 nearly an inch long, they were so inconspicuous that the first time I col- 

 lected them I examined some of the spikes several times before locating 

 certain larvae; and the next day I was surprised to see still others crawl- 

 ing about in the jar that I had not found previously. 



GENERAL CHARACTERS: THE PUPA 

 The pupa is aerial or subterranean. This stage is passed within a 

 puparium made by induration of the larval skin; and generally retains 

 many of the characteristics of the larval stage. This .skin, I believe, 

 always becomes more or less inflated dorsally and anteriorly and shortened 

 along the ventral line. 



The larv^al respiratory structures do not seem to function in this 

 stage, at least not near its completion. The tracheae from both the 

 anterior and posterior pair become constricted off and flattened against 

 the inside of the puparium, outside of the delicate nymphal membrane. 

 In the case of Eristalis and Microdon a special pair of prothoracic 

 cornua are developed for pupal respiration; and judging from the pub- 

 lished notes, this is probably true of \''olucella, Hc/ophilics, Mallota and 

 Xylota as well. As pupation approaches in Eristalis, they appear first 

 as round dark areas of the body- wall, later pushing out to a length of 

 several millimeters. They are located on the fourth body-segment or 

 the body-segment just posterior to the one bearing the anterior larval 

 respiratory cornua. The latter also elongate but always remain shorter 

 than the pupal cornua. The pupal structures connect internally with 

 trachea which clearly lead to the dorsal part of the prothorax of the 

 developing adult, ( vSee Fig. 146a, Plate VII j. Wheeler states in discussing 

 M. tristis, "When the time for pupation arrives .... a pair of short 

 tubercles or protuberances make their appearance near the anterior end 

 in addition to the single respirator}' tubercle at the posterior end." It 

 will be recalled that anterior larval spiracles have not been demonstrated 

 for Microdon. 



