32 SOUTH-AFRICAN BUTTERFLIES. 



country.^ As I suggested in the place cited, there is an evident con- 

 nection or relation between these wonderful migrations of certain species 

 of Pierincv and the well-known habit of nearly all the members of the 

 Sub-Family of flying straight onward in one direction. If it is the 

 case that males only compose some of the migrating hosts, the wider 

 distribution of the species concerned would not in such instances be 

 promoted ; but where both sexes are represented it cannot be doubted 

 that these multitudinous invasions of fresh territory must considerably 

 widen the area occupied by the species ; and it seems probable that 

 the world-wide prevalence of the Fierince, and the immense range of 

 such genera as Callidryas and Colias, have been largely aided by both 

 the ordinary and extraordinary travelling tendencies of these butterflies. 

 It may be added that when (as seems not seldom to be the case) these 

 vast flocks wing their way out to sea, although as a rule destruction 

 must sooner or later overtake them all, yet occasional stragglers of such 

 powerful flyers may occasionally reach oceanic islands, and possibly 

 succeed in establishing their species there. It is true that the swifter 

 and lighter males would be more likely to profit by any remote chance 

 of reaching such a haven, but it is not impossible that a female may 

 now and then succeed in doing so. A passing ship may sometimes aid 

 in this dispersal of a species ; for I have seen Pyrameis Cardtci, the 

 most widely-distributed species of butterfly known, fly on board a vessel 

 ninety miles to the west of Teneriffe, and after a short rest start ofi" 

 westward again ; and on another occasion, 195 miles west of Sierra 

 Leone, I captured (among numerous other insects that flew on board 

 the steamer " Norseman ") ten specimens of butterflies belonging to 

 the Sub-Family JSatyrince.^ 



6. Protective Resemblances and Mimicry. 



The prevalence in Nature of disguises protective to the wearers is 

 matter of observation everywhere, and is particularly noticeable among 

 the varied and multitudinous tribes of insects. In a world where com- 

 petition is intense, where the relations between organic beings are of 

 infinite complication, where it is the lot of the favoured few only to get 

 enough to eat and to avoid being eaten, the advantages of escaping the 



^ Mr. Barber in i88l sent me a graphic account of the extraordinary abundance of this 

 Callidryas during that season in Griqualand West. The caterpillars were observed in thousands 

 on Cassia arachnoides, a very abundant plant there. They stripped it entirely of leaves, 

 and then devoured the young shoots, and even the bark of the stems. In March and April 

 the butterflies appeared in myriads ; but in the height of their greatest abundance there 

 came a week of cold and very wet weather, which reduced their numbers very considerably. 

 This case is instructive, indicating how the migration in force of species of this genus is most 

 probably occasioned by their having as larvae exhausted the supply of their proper food-plant 

 in a tract where circumstances had favoured their excessive multiplication. 



2 This was a remarkable case, for the butterflies in question were slow-flying shade-fre- 

 quenting species of Melanitis and Mycalesis, which haunt dense woods and thickets, and 

 avoid the open sunshine altogether. The wind on this occasion, though from the eastward, 

 was not at all strong ; the time was noon. 



