In Hydropsyche (Fig. 448) the tracheal gills persist throughout life, while in other genera they only last through the pupal stage. When first hatched, the larva of Phryganea lacks gills. The larvæ of most of the Hydropsychidæ, Rhyacophilidæ, and Hydroptilidæ have no gills, though they appear well developed in the pupal stage. (Klapálek.)
Fig. 447.—A, an abdominal segment of Hydropsyche, with the tracheal gills (lbr): trl, longitudinal tracheal trunk; f, stigmatal branch. B, 5th abdominal segment of pupa of the same; l, the three lateral flaps of the tergite; br1, br2, branchiæ.
Fig. 448.—Imago, abdominal segments IV to VI, with the gills at a concealed in their natural condition; at b, drawn out with the needle; at c, projecting abnormally and dried.—This and Fig. 447 after Palmén.
Fig. 449.—Larva and pupa of Paraponyx stratiolata, enlarged; s, spiracle.—After De Geer (compare Hart’s figure of P. obscularis, living in the Illinois River).
The only lepidopterous larva known to be provided with tracheal gills is that of the pyralid genus Paraponyx. Its thread-like gills, arranged in tufts of three or four, arise from a common tubercle situated on the sides of nearly all the segments. Wood-Mason describes the East Indian P. oryzalis as “covered with a perfect forest of soft and delicate white filaments,” arranged in tufts disposed in four longitudinal rows. “The stigmata of the 2d, 3d, and 4th abdominal somites only are clearly discernible.” The caterpillar crawls “free and uncovered” over the submerged leaves of the rice plant “in the very midst of the water.” In a Brazilian species of Paraponyx described as Cataclysta pyropalis, by W. Müller, the tufts are reduced to simple unbranched filaments, and the case is more complex than in the European species (Fig. 449).
Fig. 450.—Anterior end of larva of P. stratiolata, showing the head and first two thoracic segments, with their gills: A, a tuft of gills, much enlarged.—After De Geer.