TRANSPARENCY IN WINfiS OF I.KI'IDol' I KKA. 83 



Transparency in wings of Lepidoptera (>rith jdatc). 



By WILLIAM J. KAVE, F.E.S. 



This is a phenomenon that has been observed somewhere or other 

 by every lepidopterist. The bee-like hawk-moths, Hemaris fitcifoDiiis 

 and Heniaris tityiis, the Sesiidac or .Eiferiidae, and, to a less extent, 

 Spilosdiiia iiioulira in the $ , will be at once recalled by every British 

 entomolof^ist. But no idea can be gained as to the widespread occur- 

 rence of transparency until one conies to South America. Nowhere 

 else in the world is the phenomenon so marked or does it occur in so 

 many families or subfamilies. It there occurs in some form or other 

 in every butterfly faujily, riz., rajiilinnidac, Eii/ciiiiihtt', Sati/ridac, 

 Nyinplialiilae, Hesperiidae, as well as in the Spliiwjidai', Sijutoiiiiilac, 

 Arctiidae, Geoinetridae, Zj/i/aenidae, Pijralidae, hi/psiilac, < 'axtniidac, 

 and A%(ieriidae. It is, however, remarkable that, so far, clear-winged 

 bee-like Sphiiii/idae are not known from the region. 



In the Sjdiiwiidae and Ztjuacnidae one finds greater development 

 towards transparency in other countries, notably in North America, 

 Europe, and in India, while the Sipitomidac, for their numbers, have 

 developed the tendency far more in the tropics of the Eastern Hemis- 

 phere than in the West, but even though the character is less general in 

 this family, in South America, and occurs in a smaller percentage of the 

 forms, it is, in certain instances, far more complete than in any old 

 world species. The general questions of transparency seem to be: 

 (1) Why has it come about ? (2) How has it come about ? The first 

 is probably far more easily answered in a general way than the second. 

 Without doubt, transparency in many forms ofi'ers protection to those 

 species that develop it. It may be that one species develops transparency 

 to be like many another insect that is already transparent, and thus gains 

 protection by entering a Miillerian association. In another, a hawk- 

 moth assimilates a bee and a Batesian mimetic resemblance is made, 

 the moth escaping under the guise of an unpalatable bee. Again, a 

 Syntomid moth is like a fly or wasp, and a clear- winged ^Egeriid derives 

 the same protection. 



There is probably, however, a third reason why it is beneficial for 

 certain lepidoptera to become transparent. By losing their scales 

 some insects could become more powerful on the wing and thus in 

 themselves rely on more protection from birds and bats. A ridged 

 surface, such as is presented by a scaled wing, must ofi'er more resistance 

 to the air than a comparatively smooth surface. In the case of the 

 transparent Hemarine hawk-moths, probably both the rapid flight 

 and the resemblance to a bee were caused by the simple process 

 of losing and modifying the scales. I have already mentioned how 

 many species have apparently become transparent so as to conform to 

 other species that were already transparent — species that have entered 

 a Miillerian association of transparent-winged forms — but, primarily, 

 the models or earliest transparent members of the group must have 

 adopted this phase for very difi'erent reasons. In certain cases, such 

 as Mct/mna roufiisa, in the Ithoiniinac, the transparency has, coupled with 

 the intense black margin and transverse bars, probably given the insect a 

 more pionounced conspicuousness and offensive look. In other cases, 

 such as those in the genus It/iunn'a, transparency has given them a more 

 or less inconspicuous aspect on the wing, so that they do not convey 



April 15th, 1905. 



