480 



OTHER HLCHJD-SUCKING FLIES 



e^c — 



first segment (Fig. 222 prol.) is used for creeping, in conjunction 

 with the posterior sucker, the larva looping along like a " meas- 

 uring worm"; it is also of use in constructing the silken cocoon 

 from the secretions of the salivary glands. This single little 

 leg has a crown of tiny hooklets which make it possible for the 

 possessor to hold its ground even in a torrent of water. The 



salivary glands referred to are quite 

 unlike those of other insects, in that 

 they extend clear back to the pos- 

 terior end of the body (Fig. 222, sal. 

 gl.). The fluid secreted hardens to 

 silk at once on exposure to water, 

 and is used not only in spinning the 

 cocoon, but also in spinning anchoring 

 1 breads and life-lines. According to 

 Malloch, the larva when disturbed 

 releases its hold and floats downstream, 

 holding by the stumpy leg to a silken 

 thread which is being spun out, and 

 ])y means of which the insect later 

 regains its former position. The 

 larvse breathe by means of tiny gills 

 whieli can be projected through a slit 

 in the last segment of the abdomen 

 (Figs. 221 and 222, an. g.). The larvae 

 are never found solitary, as would be 

 expected from the manner of laj'ing 

 eggs; the author has seen the boards 

 dJK. tr., diRcstive tract; m. f., on the bottom of a log chutc com- 



posterior sucker; sal. gl., saii- of these larvo} for areas of a square 



vary and .spinning gland. ^^^^ ^^ ^^^^ 



After four or five weeks, in summer, the larva? prepare to go 

 into the resting pupal stage, and spin for themselves a partial 

 cocoon which is variou.sly shaped like a jelly glass, slipper, wall 

 pocket, etc., oi)cn at Ihe upper (mkI for (he extrusion of the 

 l»raiiching gill filaments which are u.scd as breathing organs (Fig. 

 22 IC). Some species simply spin a snarl of threads, the work 

 of a whole conmiunity, in the meshes of which the pupte exist in 

 a fair state of protection. The general form of the pupae can be 



an.^ 



post. 3, 



Fig. 222. Larva of black- 

 fly, Simuliufri icnu.stum, side; 

 view .showing some of internal 

 anatomy; an. g., anal gills; 



