Flies 229 



formed in the mud of the shore. The tiny black eggs 

 (fig. 138) are laid in close patches on the vertical stems 

 or leaves of emergent aquatic plants. 



Black fly larvae live in rapid streams, attached in 

 companies to the surfaces of rocks or timbers over 

 which the swiftest water pours. They are blackish, 

 and often conspicuous at a distance by reason of their 

 numbers. They have cylindric bodies that are swollen 

 toward the posterior end, which is attached to the 

 supporting surface by a sucking disc. Underneath the 

 mouth is a single median proleg, and on the front of the 

 head convenient to the mouth, there is a pair of *'fans," 

 whose function is to strain forage organisms out of the 

 passing current. The full grown larva spins a basket- 

 like cocoon on the vertical face of the rock or timber, 

 and in this passes its pupal stage. The eggs are laid 

 in irregular masses at the edge of the current where the 

 water runs swiftest. 



In like situations we meet less frequently the net- 

 winged midges (Blepharoceridae) , whose scalloped flat 

 and somewhat limpet-shaped larvae are at once recogniz- 

 able by the possession of a midventral row of suckers 

 for holding on to the rock in the bed of the rushing 

 waters. The naked pupa is found in the same situation 

 and is attached by one strongly flattened side to the 

 supporting surface. 



These five above-mentioned families are the ones 

 most given over to aquatic habits. Then there are 

 several large families a few of whose members are 

 aquatic: Leptidae, whose larvae live among the rocks 

 in rapid streams, hanging on and creeping by means of 

 a series of large paired and bifid prolegs; Syrphidae, 

 whose larvae are known as "rat-tailed maggots" since 

 their body ends in a long flexuous respiratory tube, 

 which is projected to the surface for air when the larva 

 lives in dirty pools ; Craneflies (Tipulidae) see fig. 2 1 5 on 



