August, 1944 



Ross: Caddis Flies of Illinois 



117 



Macronetnum transversum (Walker) 



Hy dropsy che transversa Walker (1852, p. 

 114); 9. 



Macronema polygrammatum McLachlan 

 (1871, p. 129); d^.' 



Macronema polygrammaticum Betten (1934, 

 p. 204). Misspelling. 



As in the case of Carolina, we have not 

 yet taken this species in Illinois but have 

 found it in small numbers in the White 

 River at Shoals and Petersburg, Indiana. 

 We have not actually reared the yellow- 

 headed larva of this genus which we are 

 considering as this species. By a process of 

 elimination, however, there seems no ques- 

 tion as to the association. This larva, fig. 

 417, differs from the others not only in 

 color but in having the posterior portion of 

 the head ridge produced into a pair of 

 tubercles. 



Little is known regarding the distribution 

 of the species. Available records are from 

 Georgia and Indiana. 



HYDROPTILIDAE 



This family comprises most of the "micro" 

 caddis flies. Various members of the family 

 frequent diverse situations, and in Illinois 

 one or more species may be found in al- 

 most any unpolluted lake or stream. Every 

 known Nearctic genus has a representative 

 in the central or eastern states. 



The adults are hairy and usually have a 

 mottled pattern; the maxillary palpi are 

 five-segmented in both sexes and the wings 

 have either reduced or compressed venation. 

 The pupae, fig. 44, are very uniform in 

 structure and no characters have been found 

 to key them to genus. 



The larvae are unique in possessing a 

 modified type of hypermetamorphosis. In 

 at least some genera (see Ochrotrichia, p. 

 125, and Mayatrichia, p. 160) the early in- 

 stars have a slender body fitted for free, 

 active life and have no case. These forms, 



'422 



423 



Fig. 422. — Mayatrichia ayama, apex of ab- 

 domen of early instar larva. 



Fig. 423. — Ochrotrichia sp., apex of abdomen 

 ot earlv instar larva. 



fig. 557, have a slender abdomen with the 

 dorsum of each segment sclerotized. The 

 Mayatrichia larva studied has structures 

 similar to the mature form, fig. 422, but the 

 Ochrotrichia larva differs in having long 

 tarsal claws and long anal legs and claws, 

 fig. 423. Later instars make a case and are 

 modified for life in a case; the abdomen 

 enlarges, at least some tarsal claws are 

 stout, and the anal legs and hooks are re- 

 duced to small, stout hooks. Early instars 

 are known for very few genera. Perhaps 

 because they are exceedingly minute (about 

 1-2 mm. long), they are seldom collected. 



The larvae and cases possess many gener- 

 ic characters and few specific characters, 

 so that in the treatment of this family the 

 generic characters are described in some 

 detail under the first species in each genus. 



Many of the genera of the Nearctic 

 Hydroptilidae occur throughout the Ameri- 

 cas, frequently with as many species in the 

 Neotropical region as in the Nearctic, or 

 more. Much pioneer work has been done 

 in the study of the Neotropical fauna by 

 Mosely, and the North American students 

 of the group will find much valuable mate- 

 rial in his two papers on the Mexican and 

 Brazilian Hydroptilidae (Mosely 1937, 

 1939). 



KEY TO GENERA 

 Larvae 



1. Abdomen enlarged, at least some part 



of it much thicker than thorax, figs. 

 541; 5575, living in case (later in- 

 stars) 2 



Abdomen slender, not appreciably 

 thicker than thorax, fig. SSI A; free 

 living, not with case (early instars) 

 not keyed 



2. Each segment of abdomen with a dark, 



sclerotized dorsal area, figs. 449, 



464^ 3 



Abdomen with at least segments 2-7 

 without dark, sclerotized dorsal 

 area, at most with a small, delicate 

 ring, fig. 4645 4 



3. Abdomen with dorsal sclerites soHd; 



segments 1 and 2 small, 3-6 greatly 

 expanded, fig. 449. Case translu- 

 cent, ovoid and water-penny shaped, 



fig. 450 Leucotrichia, p. 120 



Abdomen with dorsal sclerites mem- 

 branous across middle, fig. 464.-/; 

 segments 1-6 evenly expanded, as 

 in fig. 541 Ochrotrichia, p. 125 



