6 FAUNA HAWAIIENSIS 



species in these groups being in a very unstable condition. The variation is not 

 confined to differences in size, colour, &c., but affects important structures, in which 

 it is unusual to find any noticeable variability, and to this is due the extreme difficulty 

 of determining and describing the numerous species, the specific characters frequently 

 having to be taken from structures which are obviously variable. 



In striking contrast with the groups above mentioned are the species of Odynerus. 

 Very few of the 86 species exhibit any variation of note, and this when it occurs is nearly 

 always of an unimportant character (e.g. colour). From this one would infer that the 

 Odyneri have now reached the maximum of species that the islands can support, in the 

 present condition of the Lepidopterous fauna, on which, as they prey on caterpillars, 

 they are dependent. The Bees on the other hand are not similarly restricted, for 

 with flowers abundant at all seasons, the islands so far as one can see, are capable of 

 supporting much greater numbers of these than of Wasps. The Fossores, which 

 like the wasps are predatory, living on Dipterous insects, are very variable, but the 

 total number of species of these is insignificant compared with that of the Odyneri. 



The coloration of the Aculeata of the islands is very remarkable. No one 

 examining an extensive collection of these could fail to remark the general blackness of 

 these insects. In the majority of the endemic species the wings are dark, with blue, 

 violet, or purple iridescence, and such species are found in each division of the group, 

 and in every genus. For this reason many of the Fossores, Bees, and Wasps, when 

 on the wing, greatly resemble one another and can hardly be distinguished except by 

 differences in their flight. It is not probable that this similarity of appearance has any 

 protective significance, for some of the species which are clear-winged and of ordinary 

 appearance are amongst the most abundant, and birds which alone could be their 

 enemies, neglect both alike. 



In the case of the genus Odynerus the coloration of the species presents some 

 remarkable features. Thus excepting one coast species, all the Kauai forms are 

 similarly coloured, having two white or yellow abdominal bands. On all the other 

 islands only a very few species are found with these markings, and in general the 

 bands, when they occur, are much less conspicuous. In spite of the identity in 

 general appearance of the Kauai insects they are often structurally very remote from 

 one another. Thus O. nigripennis, a black-bodied Wasp of large size, found on all the 

 islands from Oahu to Hawaii, is represented on Kauai by O. radida, with the yellow 

 bands characteristic of the species inhabiting that island. Again O. keterochrojims, a 

 black species found on Hawaii and very remote structurally from O. nigripennis, is 

 also represented on Kauai by a species with two yellow bands, and so on in other 

 instances. On Molokai a very large number of species have red markings. Two 

 species found in company on Oahu, O. oa/mensis, and O. psendochromtis, are excessively 

 alike in superficial appearance, and unlike any other species, being both remarkable for 

 their hyaline wings, and peculiar red markings ; yet structurally they are not allied to 



