xcvi ' FAUNA HAWAIIENSIS 



with dark iridescent wings ; and, when other groups of Hymenoptera are considered, is 

 swelled by species of bees, of fossorial wasps, and even of parasitic Ichneumonoids. 



It is clear thdt the colour phenomena exhibited by our Hawaiian Hymenoptera are 

 similar to those seen in other countries (whether in the Hymenoptera or in other orders) 

 where such colour groupings are explained as being associations of inedible species, 

 which are easily recognized by predatory enemies from their similarity of colour. 

 Whether this explanation is true in the Hawaiian case is, I think, very doubtful, though 

 I do not doubt that a satisfactory explanation of this would also explain the others. 

 The Australian Eumenidae, Prosopidae and Fossorial wasps furnish instances very 

 similar to the Hawaiian, and in the same groups, as I have myself observed in the 

 field, in that country. I feel considerable difficulty in the existence of four well-defined 

 colour groups, the members of which more or less intermingle in locality on the small 

 island of Oahu. Were each of these groups composed of members the most closely 

 allied structurally to one another, the difficulty would appear less ; but it is far otherwise, 

 for the species of the distinct genus Nesodynerus are divided amongst Groups I and H, 

 containing structurally diverse forms of Odynerus, and the remarkable Group HI 

 contains three quite different structural groups of the latter genus. On one occasion 

 all the six members of this group were taken in the same spot and on the same day, and 

 it is common to find two or three of the species flying in company, the number of 

 individuals of each species varying according to place and season. In all the groups 

 some of the species are always very much less numerous in individuals than others. 

 Instead of becoming split up into four colour groups on Oahu alone, one would have 

 supposed that it would have been more profitable and easy for one group only to have 

 formed, as being more easily recognized. As it is, one certainly cannot say that one of 

 these groups is more successful than another, for each contains extremely common and 

 comparatively rare species. It may be noticed that, excepting two species (hardly to 

 be reckoned as forest-insects, being probably recent derivatives from very similar forms 

 on other islands) the Kauai wasps have practically become superficially all alike, and, 

 as has been remarked, there is a strong tendency in the direction of a single colour 

 group on Hawaii. 



If we assume that these colour groups are formed by processes of natural selection 

 and are indicative of inedibility, we are perplexed as to the immunity of insignificant 

 forms, which do not attain notably iridescent wings or any markings, and yet fly around 

 in company with these others and are equally or sometimes even more plentiful. For 

 if these are successful, why should colour groups occur at all ? It is fair, however, to 

 say that the one instance in which an aculeate was taken from the stomach of a bird, 

 was that of a diminutive male of Nesomimesa, one of the most inconspicuous forms, 

 extracted from the thrush Phaeoj^nis lanaiensis. It should be added that the writer 

 collected series of nearly every land-bird on each island, and so was able to examine 

 the stomach contents of a large number of birds in all, and the finding of a solitary 



