INTRODUCTION xcvii 



Mnnesa only, would not tend to show the Hymenoptera, as a favourite food, in any 

 shape or colour. As a matter of fact, an Aculeate Hymenopterous insect (with rare 

 exceptions) is so unlike that of any other order by its general appearance in life, that 

 one can hardly imagine any vertebrate enemy with sense enough to distinguish between 

 colour groups of these and without the sense to distinguish the class as a whole. If 

 colour groups in Hymenoptera have arisen as a mark of inedibility, the latter quality 

 can I think have nothing" to do with the possession of a sting. 



At one time I supposed that the Hawaiian colour groups might be the result of the 

 action of climatic differences, at least in so far as these groups were special to certain of 

 the islands. This seems very doubtful, for we find the nearest approach to the colour 

 group of wasps living in the forests of Kauai, in those living on the driest coasts of 

 Oahu, and quite absent from its very similar forests. In fact a satisfactory explanation 

 of the colour groups of Hawaiian Hymenoptera is wanting, and, when found, will no 

 doubt explain some of the similar phenomena elsewhere. 



It is interesting to trace the structurally allied forms on different islands and see 

 how their superficial appearance is changed by entering different colour groups. 



Odynenis eutreius of Hawaii is a black insect with dark blue-iridescent wings ; on 

 Maui it is represented by O. homoeogaster, a red-marked wasp ; on Kauai by O. viimus, 

 a conspicuously white-banded species. The obscure-t>7uictatiis group on Hawaii is 

 replaced by the redder species O. sandzvichiensis and its allies on the intermediate 

 islands ; on Oahu the blue iridescence of the wings is lost as well as all the red markings 

 {p. dubiosus and allies), while on Kauai the red markings remain, but the wings are of 

 a shining fuscous [O. blackbiirni and soror) as in the Oahuan allies. Odynerus nigri- 

 pennis, ubiquitous over all the other islands, is replaced on Kauai by the banded 

 O. radii la. 



From what has been said above, it appears that Hawaiian Odynerus have little to 

 fear from vertebrate enemies, but in all localities (more or less), at times, a failure of 

 food supply occurs. This is of course most marked in dry coastal districts, where, in 

 some unusual seasons, vegetation never advances sufficiently, for a whole year or more, 

 to furnish food for the caterpillars, which are the prey of these wasps. The same 

 climatic causes, however, which retard the emergence of the Lepidoptera, until suitable 

 weather returns for the growth of the food plant, cause the Odynerus to lie dormant in 

 the larval stage and await the same conditions before pupation takes place. But for 

 this, many of the littoral species would, no doubt, be quickly exterminated by occasional 

 unusually dry seasons. The larvae of the Odyneri are attacked by a minute Mirine 

 Encyrtid of the Chalcid series, and since such different species as O. nigripennis, 

 montanus and oaliuensis have been found to be destroyed, it is quite likely that many 

 others are subject to its parasitism. This parasite was not noticed until 1901, when it 

 was bred from O. oaliuensis from the Makaha valley, but there is no good reason to 

 suppose it to be of recent introduction, as up to that time few Odynerus had been bred. 

 F. II. I. n 



