MIGKATION AND DISPERSAL OF INSECTS: LEPIDOPTEKA. 125 



February, i.r., in the early months of the westerly monsoon, 25 of the 

 80 cases enumerated thus occurred, and the others, made from memory, 

 must not be taken too literally. Moore, he says, also observes that in Cey- 

 lon the migration flights usually commence in November. Piepers sus- 

 pects that the flights are annual, but that they are not specially noticed 

 except in those years in which the species are especially abundant, and 

 that this condition arises when there has been an early and a very dry 

 easterly monsoon, the flights being more general in the very early part of 

 the rainy season accompanying the westerly monsoons. During these 

 migrations the butterflies fly rapidly, going straight ahead, not turning 

 aside, but surmounting all obstacles that may be opposed to their 

 progress, continuing their movement in a direct line, never stopping 

 at flowers for food. It is this manner of flight that is abnormal, the 

 continued onward movement, as if for a definite purpose, being very 

 different from that in which the insects ordinarily indulge ; they cease 

 flying, however, when there is rain or no sun, just as they would were 

 they not making these definite journeys. The insects, Piepers states, 

 follow no definite direction, they usually fly with the wind, but 

 occasionally, if the wind be weak, they have been observed to fly 

 against it. Thus Zeper and other observers note the flights in 1877 

 and 1879 as being with the wind ; Backer notes in 1882 swarms 

 coming Avith the wind from the marshy districts in the interior of 

 Sumatra, but changing their direction and following the shore when 

 the coast was reached. Piepers states that the 1883 migration that 

 he himself observed in Java, and which extended over six to seven 

 weeks, was easterly in direction and with the wind. On the other hand 

 Zeper states that one flight observed in 1877, in Java, was towards the 

 south-east whilst the wind blew from that quarter. In diflerent times 

 of the same season the direction varies. Thus Kerkhoven observed, in 

 January, 1889, that the insects flew from west to east, but on February 

 2nd or 3rd, when they were again noticed, they flew from south-east 

 towards the north-west. So also Ottolander observed in 1885 that 

 Ki(j)l(H'a einticc at first travelled towards the east, but a dozen days later 

 towards the west. Concerning the fact that butterflies do fly against the 

 the wind, Piepers notes that Marott states {Fcuillc da^ Jcidws natiiralistt'.s) 

 that in the month of September, 1872, he met out at sea, a column of 

 l\i/rai»t'u carditi struggling boldly against the wind, but that, in spite 

 of their efforts, many were continuously beaten back into the water, 

 where they perished in such numbers as to give the sea the appearance 

 of a pond covered with leaves. Piepers observes that Zeper had written 

 that he had often seen isolated butterflies as well as swarms of them 

 flying from the land out to sea at a considerable distance from the 

 shore, but he added that if the wind fell, they at once changed their 

 direction and attempted to regain the shore. He also observes that 

 on the shores of Holland large swarms of lepidoptera have been noticed 

 arriving from a sea journey, and so fatigued by the journey, that 

 immediately on arrival they have settled on the shore and the dunes 

 to rest in such numbers that the road has been covered with them. A 

 somewhat parallel instance is noted by Piepers as occurring at Siak, in 

 Sumatra, in Septem1)er, 1880, but, in spite of the well known fact 

 that migrating butterflies in Ceylon, nearly always head against the 

 wind when on their periodical flights, Piepers insists that the butter- 

 flies observed migrating in the East Indies fly with the wind, and 

 that they cannot fly against it, except it be very weak. 



