Colour- groups of the Hawaiian Wasp>s, etc. 685 



striking, nearly half the known species being so coloured. 

 Group IV on Oahu ( = II of Maui, etc.) is not very clearly 

 marked off from its Group I, when the insects are seen in 

 flight, but, as they usually have a characteristic grey or 

 hoary appearance, they may be kept apart, especially as 

 they represent species mostly peculiar to open country or 

 open spaces in forest country. When their representatives 

 on Hawaii are considered, they become much less distinct 

 from those representing Group I on that island. 



Groups II and III on Oahu are peculiar to itself, the 

 dull red markings, clear wings and body clothing of the 

 former giving them, dead or alive, an appearance unlike 

 anything else, and the shining fuscous wings of the latter 

 rendering these equally unmistakable. 



In a few cases, isolated species have been found on 

 islands, where they ill accord with the groups there repre- 

 sented, but one cannot overlook the probability of these 

 being recent immigrants. Thus 0. /rater, Dalla Torre, a 

 widely distributed species, has been found very rarely on 

 Oahu, where it does not fit into any Colour-group, as it 

 does on Maui, where it abounds. Excepting on Kauai, the 

 Group I of Oahu is well represented on every island, 

 besides tending to absorb all others on Hawaii, so that 

 nearly half the known species of the wasps may be referred 

 to it. The dominance of this group increases the black- 

 ness of our series, for it contains species almost or entirely 

 black and 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. 



"In these associations of Aculeates, the Eumenidae are 

 probably dominant, although both the Fossores and bees 

 are extremely ancient. In the Crabronidae several genera 

 have been evolved probably from a single ancient immi- 

 grant species (see p. 688). Over fifty species of Nesoprosopis 

 fall into structural groups of which one has become para- 

 sitic (inquiline) on the others and has lost the special 

 pollen-sweeping apparatus on the front tarsi. Five of these 

 inquiline species have been produced, of course from one 

 original. The three most yellow-spotted species of Grabro, 

 which always have a yellow-banded abdomen, are found on 

 Kauai with the yellow-marked Odyneri. Two of these 

 Crabros extend to the other islands, or some of the other 

 islands, but one of these, on Oahu, is tending towards 



