INTRODUCTION Ixxj 



XXIX 



noticeable in Honolulu in 1903, but was not taken in 1900, when I collected a number 

 of specimens of the other two species in gardens there. This recently introduced 

 species now far outnumbers the other two combined, in Honolulu. It has different 

 habits, in that, instead of nesting in burrows or cavities in woodwork, it forms mud- 

 cells like those of Sceliphron, fixing these under ledges and on the walls of wooden 

 houses, etc. The other two Pison are older introductions, both having occurred at 

 Blackburn's period of collecting ; both are apodemic and of Australasian origin. All 

 the species, like Trypoxylon, store their nests with spiders. It is perhaps worthy of 

 note that the Trypoxylon was introduced first into Hawaii, and not through the port 

 of Honolulu, as has usually been the case with imported insects. It did not reach 

 Oahu until some years after it had become widely spread and abundant on the large 

 island. 



Sphegidae. — Represented only by the imported American Sceliphron, an universally 

 distributed species in the islands, from the coast to 2000 ft. and sometimes higher 

 elevations. It varies much in colour, as is the case in its native home. It is an 

 injurious species, in that it disfigures the walls and ceilings of houses with its large 

 masses of mud-cells. In the country these mud-cells are placed on rocks and trees, and 

 whether in the houses or outside are frequently occupied by the introduced Pison or the 

 endemic Odynerus nigripennis, more rarely by other species, as nests for their young. 

 On Kauai O. radula also occupies the disused cells of Scelipliron. 



EuMENiDAE. — This family is represented by a greater number of species than any 

 other of the indigenous Hymenoptera, and all, to the number of 102, belong to the 

 ubiquitous genus Odynerus, sensu latiori. From this interesting complex I have split 

 off some small groups of species and considered them as distinct genera, as indeed they 

 are, although they appear to be derivatives of the same stock, as the Hawaiian Odynerus 

 proper. Odynerus nigripennis and its three allies are of different descent from that of 

 all the others, and certainly are sprung from a quite different' ancestral immigrant. If 

 the classification of the Odynerus of the world were not in a chaotic state, these four 

 species would not be placed in the same genus as the others, and a number of genera or 

 sub-genera, allied to one another, would also be formed for the dispersion of the bulk of 

 the Hawaiian species. One might reasonably compare the Hawaiian series of Odynerus 

 with that of the Nitidulidae in beetles. Though the known species are less numerous, 

 and the specific characters much more distinct, they form a somewhat similar series 

 of generic or sub-generic groups. The preciseness of the specific characters is itself an 

 interesting fact, almost indeed unique in our Fauna, when large genera like Odynerus 

 are in question. I think this distinctness of the species is quite real, and not at all due 

 to the fact that the Odynerus have probably had more time given to their study than 

 ' No doubt Asiatic ; since allied Japanese species exist. 



F. H. I. m 



