262 THR entomolociIrt'r record. 



additions and captures than I have been able to keep myself recently, 

 to check the list, and thus ensure oreater completeness and accuracy. 

 It will, however, I doubt not, form a good basis on which some 

 lepidopterist with more leisure, and a more detailed acquaintance with 

 recent work done in the micro-lepidoptera abroad, can make a catalogue 

 of purely British species, varieties and aberrations, when such a thing 

 is again wanted. If some such lepidopterist will make a copy of the 

 list, and, having added his critical emendations, send it on to Dr. A. 

 Russel Wallace, he will, I am sure, be as delighted as I. 



Migration and Dispersal of Insects : Final Considerations. 



By J. W. TIJTT, F.E.S. 



We have now passed in review a large number of the published 

 facts relating to the migration and dispersal of insects, and one 

 suspects that some attempt should be made to discover if the facts 

 throw any light on the cause of the migration or dispersal habit which 

 evidently exists in many insects. 



The facts appear to prove conclusively that there is, in many insects, 

 a strong tendency for the imagines to spread from the area in 

 which they have lived as larvie, and there seems to be no doubt 

 that, in the case of orthoptera and coleoptera, the essential reason 

 of dispersal is in order to seek new feeding-grounds ; some, at 

 least, of the movements of aphides, appear also to be largely 

 intimately connected with food-supply. In the case of the odonata 

 no such direct reference to food conditions is possible, and it is 

 distinctly evident that these do not directly influence the movements 

 of lepidoptera in the imaginal state. It is possibly not unfair 

 to suggest from the evidence that the mass movements of 

 odonata are due to the necessity of finding new breeding-grounds, 

 those in which they themselves existed as nymphs being 

 dried up and no longer affording the necessary conditions for egg- 

 laying. To a limited extent, perhaps, this may also be true of 

 lepidoptera, but one suspects that the extent to Avhich this may apply 

 is exceedingly small. We have already noted that Piepers considers 

 the migrating impulse is due to certain unexplained sexual conditions, 

 which act as a j^riraary motive force on the organism and cause it to 

 undertake long flights from its native locality, but we do not see much 

 evidence in support of this view. 



In the hymenoptera, as we have already suggested, the cause 

 of the various dispersal movements appear to be varied and 

 possibly connected in some cases with the necessity of flnding 

 a new home, in others with the necessities of cross-fertilisation, 

 and in yet others with the necessity of discovering new feeding-grounds. 

 We appear then to have, in connection with this subject, several 

 quite different phenomena to consider. 



However varied the causes may be, the general results are sinailar, 

 riz., the occupation of new breeding-grounds, the extension of the range 

 of the species should these breeding-places prove suitable, and the 

 extermination of the progeny of the immigi-ants in the course of a 

 generation or two should they prove unsuitable. The failure of 

 successive migrating bands to permanently populate a new district is 

 exceedingly well illustrated in onr comitryhy (olias cd urn and Pijrawch 



