INSECTS PREYING ON THE ORANGE APHIS. 181 



This is the commonest and one of the largest species found among 

 Plant-lice on the Orange in Florida. Certain other species, almost 

 equally common, are entirely black, and differ the one from the other 

 only in size, and in characters too minute for popular description. 



The larvae of all the species bear white flocculent tufts, and have no 

 marks by which the species can be readily distinguished. They are 

 quite active when disturbed, but are usually seen quiescent in the midst 

 of the unresisting herd of Aphis, feeding upon the young lice. 



They undergo their transformations upon the leaves among the re- 

 mains of the Aphis colonies destroyed by them and other enemies. The 

 pupa is held in the split skin of the lar^a, and is dark-colored like the 

 body of the latter. 



SYRPHVS FLIES. SYRPHID&. 



Whenever colonies of Aphis are found on the Orange there will almost 

 invariably be found among them slug-like larvae, which creep about 

 among the Plant-lice with a leech-like movement, now contracting into 

 an almost globular mass, and again elongating like the joints of a tele- 

 scope. The minute terminal joint, which constitutes the head of the 

 larva, is observed to possess a pair of retractile horny hooks, which 

 work forwards and back, in and out of the mouth, like a rake. As the 

 larva advances with a groping motion, for it is quite blind and eyeless, 

 the outstretched neck and head sweep the surface, and the jaws con- 

 tinue their raking movement until they strike the body of an Aphis. 

 Immediately the jaw-hooks grapple their unresisting victim, and soon 

 through the transparent walls of the body the sucking stomach is seen 

 pulsating and drawing through the oesophagus in a continuous stream 

 the green juices of the plant-louse. 



When actively engaged in feeding these larvae continue with the 

 greatest voracity to empty one louse after another, until they have de- 

 stroyed dozens ot them ; and their bodies, distended with the contained 

 juices, become translucent green in color. When filled to repletion, the 

 larva falls into a lethargy, lasting two or three hours ; during which 

 the processes of digestion change the juices of the body to varying 

 shades of brown, and dark masses of fecal matter gradually form in 

 the intestines. The curious changes of color in the semi-transparent 

 larvae are therefore due entirely to the condition of the body-contents. 

 Full fed individuals usually have a tinge of flesh color, owing to the 

 formation of glandular, creamy masses of fat, which have a roseate hue. 

 When fasting through scarcity of food, the fat is absorbed and the body 

 becomes dark-brown and opaque. While feeding the larva is translu- 

 cent green ; while digesting the colors change to olive and brown, with 

 distinct markings of rectdish brown and black. 



Transformations. When full fed the larva attaches itself by means 



