INTRODUCTION xliii 



Owing to our very incomplete knowledge of the insect fauna of the world, some of 

 the introduced species and also some considered to be immigrant are not yet known 

 outside the islands. The ant Prenolepis sharpii for instance, which was imported years 

 ago in boxes of plants by the Commissioner of Agriculture of the islands, and soon 

 became established and very common, was described from descendants of these im- 

 ported examples. 



In judging whether an insect has been introduced by man, when the actual fact of 

 its importation is unknown, I consider the following points. 



(i) If solely attached to foreign vegetation or parasitic or preying on imported 

 creatures only, it is certainly ' introduced,' or (less probably) ' immigrant.' 



(2) If, being a beetle or Heteropterous bug, it is found within the range of certain 

 foreign predaceous insects, it may in the case of the former be considered certainly and 

 in the case of the latter most probably 'introduced' or possibly 'immigrant' In 

 explanation of this I may state, that in the case of the truly endemic beetles, without 

 exception, and usually of the Heteroptera, the area of distribution is absolutely fixed 

 by the non-occurrence of imported predators. Owing to interference by man these 

 predators may come to occupy new areas, and then from these too the above-mentioned 

 endemic forms disappear. At first, in such cases, many of the endemic beetles will be 

 found actually being attacked by these enemies, but subsequently they will disappear. 

 Some insects, however, e.g. bees and wasps and some Lepidoptera, more or less 

 successfully resist such predators, and though endemic, can occupy the same area, as 

 also can others that rarely or never are attacked, e.g. certain Homoptera that excrete 

 honey dew. 



(3) Doubtfully endemic insects may occur outside the range of foreign predators 

 and mixed with many truly endemic ones, but usually they also range into the territory 

 occupied by the former. If not, their habits should be considered and their food, and 

 the probability of their being imported by man, but if they do so they are most likely 

 ' imported ' or ' immigrant,' and surely so if Coleopterous. 



(4) Actual affinity to, or remoteness from outside forms must always be considered. 



(5) Whether the species is isolated from other members of the fauna, or 

 whether one or more closely allied forms occur is most important. When several 

 closely related species are found in the islands the probability of their being endemic is 

 very great. Importations by man usually consist of very different insects and not of 

 closely allied species, and the same would be likely to be the case with natural immi- 

 grants. 



A careful consideration of such points in the case of any insect that is fairly well 

 studied, will usually leave little doubt as to whether it is endemic or introduced. It is 

 perhaps more difficult to distinguish the immigrants from either the endemic or the 

 imported species. We must, however, except from this statement a number of species 

 of known migratory powers, well-known species elsewhere, with great powers of 



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