164 Mr. C. B, Williams' Notes on Butterfly Migrations. 



CaUidryas eubiile has a habit of flyiiifr round and roiuid a 

 field in short strings of about half a dozen almost head to 

 tail, and closely following each other's movements. This 

 habit may throw some light on the formation of the ribbon, 

 but does not explain the movements of the leader. 



Finally, we have the extremely interesting question of 

 the sexes represented in the migration. Rodway records 

 that all that he saw were males, but I understand that this 

 was from observing their colour whilst in flight. The male 

 and female of CaUidryas eiihide differ distinctly in colour 

 and markings, and perhaps any one very familiar with 

 this species could tell them apart in this way. I found it 

 impossible to do so, and could only tell the sex after capture. 

 My specimens were, as mentioned before, seven males and 

 three females. It does seem, then, to be a general rule 

 that the males predominate, and this is confirmed by obser- 

 vations in other parts of the world. This branch of the 

 subject seems to me to be of fundamental importance, for 

 if the migrations consist so largely of males, what becomes 

 of the corresponding females ? Mr. Rodway has bred this 

 species and finds the two sexes to be more or less in equal 

 numbers, and this is the general rule for other insects 

 except in rare cases, such as parthenogenetic reproduction, 

 which seems scarcely feasible here. There remains the 

 possibility of the males developing more rapidly and 

 emerging from the chrysalides earlier than the females, 

 but there is no direct evidence for this, and against it is 

 the fact that, except perhaps at the beginning of the first 

 wet season, the successive broods of insects in the tropics 

 are ill-defined and usually overlap considerably. It may 

 be contended that the females are less fitted for long 

 flights, being heavily laden with eggs. Even if this is so, 

 we are left with the question, " Why, then, do the males 

 migrate ? " 



