INTRODUCTION Ixxxvii 



xylophagous beetles. Hylocrabro often makes its cells in soft rotten wood of such trees 

 as the Kukui [A/curih-s) or the Hau (Hibiscus). Some of the species visit flowers, 

 e.g. X. distinctus and A', uiandibjilaris, on the coasts of Oahu, Maui and other islands. 

 In the mountains they are sometimes attracted numerously by the flowers of Wik- 

 stroemiafoetida, and also those of Metrosiderus. In general, however, they are observed 

 flying round and settling on the leaves of bushes and ferns in the sunshine. The 

 females penetrate into dark shady places, so dark that they can hardly be seen, in search 

 of prey. Some of the species of Nesocrabro emit a shrill noise, when on the wing, 

 which much resembles the note of the Tachinids they are seeking. 



The series of species represented in the islands exhibits a great variety in appear- 

 ance, for some of them are much and conspicuously marked with yellow on all parts of 

 the body, the yellow markings becoming reduced in others, until in A', unicolor we have 

 an entirely black insect. 



There is in the yellow-marked species much variety in the coloration, and the 

 variation exhibited is often of an interesting character. INIany years ago Smith described 

 a Hawaiian Crabro as C. distinctus, from a specimen brought back by the old Beechey 

 expedition in the early part of the last century. Smith's description, dealing mainly with 

 colour, seemed to me to represent an insect so different from any Hawaiian Crabronid, 

 that (in the absence of the specimen, which could not be found) I suspected a mistake had 

 been made in the locality, and omitted the species from the Hawaiian list. C. distinctus 

 is now well known to me, and is an extreme and rare variety of the species I called 

 C. notostictus, which typically is a black insect, with small yellow thoracic markings. 

 Intermediate specimens between the extremes are much commoner than typical distinctus. 

 This brightly marked form has so far only been found at or near the coast, where the 

 intermediate forms also occur, as well as the variety I called notostictus. In the moun- 

 tains in the forest region the latter is predominant and intermediates are rarely met with. 

 From these facts one might suspect that the hot dry climate of the coastal regions was 

 productive of the conspicuously marked varieties. The following considerations make 

 such an explanation improbable. In the genus Nesocrabro I described a species, gaily 

 marked with yellow as A^. bidecoratus, adding a remark to the effect that "In spite of its 

 extremely distinct appearance I suspect it may prove to be a variety of the following" 

 (A^. ridirocaudatiis). This now proves to be the case, intermediate varieties having been 

 secured. The variation in this case is even more extreme than in the other, since typical 

 I'ubj-ocandatus is an entirely black-bodied insect, whereas the var. notostictus of distinctus 

 has at least yellow thoracic markings. It is interesting to observe that the markings of 

 the most highly coloured N'. rubrocaudatus (var. bidecoratus) almost entirely resemble 

 those of Xenocrabro distinctus. Looking at the localities, where these brightly marked 

 varieties of Nesocrabro occur, we find that, far from living in hot and dry places, they are 

 found in the wet woods near Kilauea (4000 ft.), in the still wetter district of Olaa and 

 other localities of windward Hawaii. I think that these highly coloured varieties are 



