180 



BLACK-FLIES. 



Constantly feeding, these larvas grow very rapidl}^, and are 

 soon ready to transform into piip^. But before they can 

 do so they have to construct some protection for the inac- 

 tive pupae, otherwise this would be swept awaj^ by the cur- 



Fig. 148. — SimuUum tribulatum, cocoon. 

 Greatly enlarged. Original. 



Fig. 149. — SimuUum tribulatum , pupa. 

 Greatly enlarged. Original. 



rent. They construct for this purpose a neat little cradle- 

 like house, made loosely of silk, and open at the top. This 

 cradle, shown in fig. 148, is built against a stone, or upon 

 submerged plants. In it the larva fastens itself by a little 

 loose silk in the closed part, and no^v transforms to a pupa^ 

 as shown in the illustration, and again, removed from the 

 cradle, in fig. 149. But a great change has taken place, and 

 the insect no longer breathes through an organ located near 

 the tail, but by an entirely diiferent one near the head. 

 These breathing-organs differ greatly in the different species, 

 but are always composed of a number of fine thread-like 

 tubes closed at the end, and which unite near the base in a 



