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 Pierince 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 Picrma;, 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 Cardui, 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 off 
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 SatT/rincc? 
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 188 1 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 arachno'ides, 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, 
^ This was a remarkable case, for the butterflies in question were slow-flying shade-fre- 
qiaenting 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 j the time was noon. 
