MIGRATION AND DISPERSAL, OF INSECTS : FINAL CONSIDERATIONS. 293 



almost all records relating to the swarming of the insect) is directly con- 

 nected with migration, has, in our opinion, no real evidence to substan- 

 tiate it. Nor is the habit at all confined to this species. Eaton notes {Knt. 

 Mo. May., xiv., p. 276) that, in the Bombay Presidency, in the latter part 

 of the " rains " (September-December), in the beginning of the cold 

 weather [i.e., the meteorological conditions being analogous to those 

 under which AuDvia arcJiippua adopts this habit) Papilio hector 

 commonly roosts in flocks. " About sunset they betake themselves to 

 trees — usually the babul (a species of gum-acacia) clinging to the 

 underside of the subpendulous branches towards their extremities, in 

 crowds of many hundreds, and there they rest until the sun is well up." 

 An almost parallel instance is to be found in the imagines of the com- 

 mon European Sati/nis hcrmionc, which, in some districts, where trees 

 are available, not only rest on tree-trunks frequently by day, but 

 even when engaged busily feasting on flowers during the hot 

 sunshine, return to the trunks and branches of the trees to roost. 

 Moftat, as we have just noted {Ilcport Knt. Sac. Ontario, 1900, 

 pp. 44 et .sr</.), disagrees with our conclusion, viz., that the data 

 at disposal do not warrant our stating that there is a southern 

 migration of Anoda arcJdppus in the autumn in North America ; he 

 adds, however, no further facts to the discussion, although he states 

 that the data that we have already published relative to this species, 

 tend to prove his point. These show a general proof, he considers, 

 that the migrating swarms slowly move southwards. As these dates 

 refer to different years, involving different conditions, and have no 

 connection with the same swarms, we are unable to follow this argu- 

 ment, and the obvious points which these dates do suggest are entirely 

 missed, c/:., that winter commences later in the more southern latitudes 

 than the northern, that, as a consequence the swarming will occur later in 

 the more southern districts, and that cold appears to be the moving factor 

 in causing the swarmmg previous to destruction in the districts out- 

 side the area that can form possible winter-quarters for the species. 

 Much more exact data are wanted before a return journey can be accepted 

 for this species, much as we would like to connect so close an analogy 

 between the migrations of insects and birds. In a later paper (loc. cit., 

 1901, pp. 78-K2), Moffat concedes much of what we urge, and there is 

 no real need in these papers to push the matter further. He notes 

 that the species cannot survive in any of the stages of its existence in 

 its northern breeding-grounds, hence, after each succeeding winter, 

 these regions where it is produced in the greatest abundance have to 

 be replenished in the spring by individuals coming from the south. 

 He has obtained from Thaxter a note supplementing his observation 

 {('an. Knt., xii., p. 38), and already quoted, to the effect that, in Florida, 

 the swarm observed was sketched on January 3rd, 1.S73, that the 

 imagines did not scatter until February, and that then many were 

 observed in coitn, thus showing that in the southern States they do 

 exactly what I'l/raineis canliii does in northern Africa, riz., live actively in 

 the imaginal state all the winter until the breeding-season arrives, and 

 then lay their eggs as soon as the vegetation is suitable for the purpose. 

 True Moffat still maintains the idea of a "return" of the northern- 

 bred butterflies in autumn, but he offers no further evidence than the 

 facts already recorded. It is a remarkable fact that P. canhii has been 

 noted as having somewhat similar habits in North America as in 



