Ixxxvi FAUNA HAWAIIENSIS 



the Hawaiian Crabronids are ubiquitous, occurring both on the coast, in open mountain 

 localities and in thick forests. Some species indeed, e.g. X. unicolor, occupy all such 

 stations, and I have found this to occur in wetter and denser forests than any other 

 wasp, and where only a few species of bees otherwise represent the aculeates. Many of 

 the species are extraordinarily numerous in individuals, and we have seen around a 

 dead cow, on which flies were abundant, a swarm of one or two species of Xenocrabro 

 almost as large as that of their prey. I several times noticed when I had shot a deer 

 on the island of Molokai, that one or more Crabronids would arrive and settle on the 

 body before this was even cold, awaiting the arrival of flies. One may well suspect 

 that at the present time the number of individuals of these wasps is much greater than 

 was the case under natural conditions of the fauna, unless, indeed, the endemic 

 Dipterous population has very much changed. The swarms of dung- and carrion-eating 

 Diptera, that now exist in the mountains, can have had no place in the original fauna, 

 and on many of these flies the wasps now largely prey. Even the common house fly is 

 not exempt, and at the Volcano-house hotel on Hawaii ^Y. atripennis has often been 

 seen entering the room and taking the flies on the window panes. If we consider such 

 flies as Sarcophaga pallinervis^ (described from the islands) to be endemic, even these 

 can now breed in numbers previously impossible, owing to the great number of cattle 

 that have been introduced, and furnish food for their larvae. Another favourite prey of 

 the Crabronids of to-day consists in two common species of parasitic Tachinid flies, both 

 foreign. 



The natural prey of the species of Nesocrabro is certainly the remarkable and 

 comparatively rare Sarcophagid flies of the endemic genera Dyscritoinyia and Prostheto- 

 chaeta. They have several times been caught, when carrying these, and a burrow of 

 A^. stygius, that was opened, was found to be packed with a small species of one of them. 

 We have taken the same flies from nests of other of the Crabronid genera, but they are 

 not restricted to these. Hylocrabro tiimidoventris sometimes provisions its cells with a 

 moderate-sized species of Drosophila. Some of the smaller species of Xenocrabro are 

 fond of preying on the Anthomyiid Lispe, and we have found others carrying species of 

 Caenosia of the same family, all these being endemic species. One species of the wasp 

 by no means restricts itself to one kind of prey, nor even always to kinds at all similar, 

 for Xenocrabro hawaiiensis on one occasion was caught carrying off Lispe and on 

 another occasion a species of the Limnobiid Dicranoinyia ! This fact is of some interest, 

 because the latter is the habitual prey of Ncsomiiiiesa ; and it shows that the Crabronid 

 can successfully capture the same without the aid of special apparatus. Xenocrabro 

 unicolor has been seen to capture and carry off the recently introduced and showy 

 Neoexaireta spinigera, a Stratiomyiid. The burrows of the Hawaiian Crabronidae 

 are usually formed in the ground ; those of Nesocrabro have been found only therein. 

 Others sometimes burrow in dead tree trunks, using, in harder woods, the borings of 



' This species is now known to be American. 



