THE AQUATIC ADAPTATIONS OF PYRAUSTA PENITALIS 



GRT. (LEPIDOPTERA).* 



Paul S. Welch. 

 INTRODUCTION. 



The unique and ingenious methods whereby aquatic animals 

 have solved their problems of maintenance are always interest- 

 ing, particularly in a group having an immediate terrestrial 

 ancestry, as is the case with aquatic insects. It is a well- 

 known fact that among insects all graduations between the 

 terrestrial and aquatic species can be found, often within one 

 family. Similar transitions are now known to exist within a 

 single species. Some of these transitional forms, while retaining 

 certain terrestrial habits and potentialities, have progressed 

 far in the development of aquatic adaptations and solve the 

 problems of the new environment with remarkable ease. While 

 Lepidoptera are preeminently terrestrial, there exists a very 

 sinall, heterogeneous group of species which presents aquatic 

 adapta;tions of. peculiar interest. The climax in ; aquatic 

 adjustment for this group is probably represented by the gilled 

 caterpiWsLTS oi '.Nymphula (Welch,. 1916). Pyrausta penitalis 

 Grt., on which ithis.ipaper is. based, .presents a striking case; not 

 only of transition from terrestrial to aquatic habit, but also 

 of a development of physiological adaptations which parallel 

 closely those appearing in certain other unrelated Lepidoptera 

 (Welch, 1914>. ' ru: -.:> m: 



The field data used in this paper were secured during the 

 summer of 1917, while the writer was a member of the Ohio 

 State University Lake Laboratory staff. In the protected 

 coves of Sandusky Bay, Lake Erie, particularly Beimiller's 

 Cove, Nelumho liitea grows abundantly and during July, 1917, 

 there appeared upon this plant large numbers of the caterpillars 

 and pupae of Pyrusta penitalis. The abundance of material 

 and the constant presence of practically all degrees of develop- 

 ment made possible a wide range of observations in a relatively 

 short time. Since the writer has spent but the one season at 



*Contribution from the Zoological Laboratory of the University of 

 Michigan. 



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