National Geographic : 1937 May
BUTTERFLY TRAVELERS cient numbers in its new home to indulge in similar mass flights, one of which was seen on the shores of Lake Ontario in Au gust. 1917. The species has also, within the last few years, been introduced into New Zealand, where it is multiplying with great rapidity. It will be interesting to see how soon mass movements occur there, and what direction they will take. Two other regular migrants in Europe are the Clouded Yellow (Colias croceus) and the Pale Clouded Yellow (Colias hyale), both of which appear to come north from southern Europe in spring and reach Britain about the end of May or the begin ning of June. Here they lay eggs which produce adults in August, but none of these survive the winter in England. There have, however, been one or two records recently of flights of Clouded Yel lows to the south in France in the autumn, so that it is possible that this species also returns to its original home. Half of the British Hawk Moths (Sphingidae) and many of the smaller moths are also migrants. The Silver-Y (Plusia gamma) and the Rush Veneer ( Xemophila noctuella) are of special in terest, as they appear in large numbers, usually at the same time as the swarms of Painted Lady Butterflies. Despite the dif ference in their size and feeding habits, there is some evidence that all three species mi grate in company. DAGGER WINGS FLY IN COLUMNS In addition to the species already dis cussed (page 571), there are a number of other regular migrants in tropical America. One of the more striking is the Many Banded Dagger Wing (Athena chiron, Plate VI, figure 6) which migrates regularly in Mexico, British Honduras, Nicaragua, Costa Rica, and Panama. It was first re corded in 1872 by Thomas Belt in his "Naturalist in Nicaragua." He writes: 'They occurred, as it were, in columns. The air would be comparatively clear of them for a few hundred yards, then we would pass through a band perhaps fifty yards in width, where hundreds were always in sight and all traveling one way. I took the direction several times with a pocket compass, and it was always southeast." Belt concludes: "The beautiful tailed green and gilded day-flying moth, Urania leilus, also joins in this annual movement." He was actually mistaken in the name he used for his species, but the two day-flying moths (Cydimon leilus and C. julgens) are perhaps the most beautiful and conspicuous of all the Central American migrants. The insect known in the West Indies as the "Green Page Moth" (C. leilus, Plate VI, figure 7) is found chiefly in Trinidad, the Guianas, and Brazil: while the closely re lated species, C. fulgens, the one seen by Belt, is known to migrate in Mexico, Nica ragua, Costa Rica, and south to Ecuador. In British Honduras the Swallowtail Butterfly Papilio philolaus (Plate III, fig ure 3) has been recorded passing in great numbers in one direction. In temperate South America many of the North American migrants reappear, in cluding Dione vanillae (Plate VI, figure 3), Ascia monuste, Phoebis eubule (Plate II, figure 3), and Vanessa carye. Charles Darwin, in 1832, saw a great flight, like a snow storm, of yellow butterflies out at sea off the Bay of San Bias, in Argentina. The flight was 600 feet high, a mile wide, and many miles long. The species is now be lieved to have been Colias lesbia (Plate III, figure 2), which is closely related to the North American Clouded Sulphur and to the English Clouded Yellow. MIGRATIONS IN AFRICA North Africa appears to be the source of a number of the European migrants and its problems are those of Europe. Tropical Africa is quite separate and has entirely different migrants in the east and in the west. South Africa appears to be closely associated with the East African area. In western Africa the two principal mi grants are Libythea labdaca (Plate VI, fig ure 9), which moves in enormous swarms in Nigeria and the Gold Coast, and Cymo thoe coenis, which has been recorded in mass flights in the Belgian Congo and Uganda. The former species has been seen moving southward about March or April. Writing of the former species, Far quharson, in 1918, said: "Early in the rains for two or three days thousands of migrat ing butterflies pass here (Ibadan, southern Nigeria), flying southward. The negro peasant knows that after that he may safely sow his cereal crops. . . . Towards the end of the rains swarms of the same butter fly return northwards. One may conclude that the rains are over." No more recent observer has reported seeing the return flight to the north.