252 REPORT OF STATE GEOLOGIST. 



relation to the environment of the insects, but are probably of value 

 in the mating of the sexes." Tlie color of the inner wings often 

 varies much in the same species, shading from dull white, through 

 yellow and orange to vermilion red. The greater intensity of color 

 is in part due to age, and perhaps in part to higher temperature, 

 though other factors doubtless enter into its cause. 



The members of this sub-family are peculiar in that the males of 

 most of them and the females of a few stridulate while on the wing; 

 a rather harsh, crackling or rattling note being produced by rubbing 

 the under surface of the tegmina against certain veins on the upper 

 surface of the inner wings. The sound seems to be under control of 

 the insect, for they often make it when suddenly alarmed, or cease 

 making it if loo greatly frightened. Some of them produce a uni- 

 form rattling note during the entire period of flight, which is gen- 

 erally in a straight course. Others make the call only during certain 

 intervals of flight. These change the direction of flight at will, and 

 at every turn emit two or three short, rattling sounds. A number 

 of species also sound a different call when at rest, in the same manner 

 as do the Tryxalince, by rubbing the hind femora against the inter- 

 calary vein of the tegmina, which is toothed or roughened to aid as 

 a sounding organ. 



This sub-family is also notable among our Indiana Acrididae by 

 having three or four species which pass the winter as nymphs or half 

 grown young. These nymphs reach maturity about mid- April and 

 are the first Acridians of large size to be seen in the spring. The 

 majority of our species, however, pass the winter, as do most other 

 locusts, in the egg stage. 



Twenty-six genera and 3 54 species were listed by Scudder in his 

 '^Catalogue," and about -10 species have since been described. Of 

 these, ten genera and sixteen species have been taken in Indiana. 

 These genera may be separated by the following table in which, how- 

 ever, I have made use of many characters not of generic importance, 

 in order that the beginner may the more readily determine the speci- 

 mens in hand. 



KKV TO OENERA OF INDIANA CKniPODIN.E. 



fl. j\I('(lian cariurt of pronoliim raised in a distinct crest, which is entire, 

 or not cut by the principal sulcus; tegmina sub-coriaceous, or leath- 

 ery, in texture, densely and irregularly reticulate; inner wings 



brightly colored, red or yellow at base XXV. Arphia, p. 254 



an. Median carina of pronotimi less prominent and in female always cut 

 by one or more sulci: tegmina with the apical half membranaceous 

 and regularly reticulate. 



