1 84 NATURAL HISTORY OF AQUATIC INSECTS CH. 



not unlike in shape to the nests of some Swallows. 

 This nest is glued fast to the surface of a water-weed. 

 The salivary glands, which furnished the mooring- 

 threads, supply the material of which the nest is 

 composed. Sheltered within this smooth and taper- 

 ing cocoon, whose pointed tip is directed up-stream, 



A B 



FIG. 65. A, four pupae of Simulium in their cocoons, attached to aquatic stem ; B, 

 pupa of Simulium, removed from its cocoon. 



while the open mouth is turned down-stream, the 

 pupa rests securely during the time of its trans- 

 formation. 



When the cocoon is first formed, it is completely 

 closed, but, when the Insect has cast the larval skin, 

 one end of the cocoon is knocked ofif, and the pupa 

 now thrusts the fore-part of its body into the current 



