DISTRIBUTE INSECT VARIETY. 305 



mated, and the females no longer gravid. Another account of 

 this phenomenon says they fly from sea to sea. The slim South 

 American Heliconice have likewise individuals that swarm and 

 migrate, for the H. narcea, Mr. Moseley informs us, covered the 

 decks of the Challenger when making Bahia in calm weather. 



That the intolerable heat of the sun, exerting its tendency 

 in amassing insects into flocks by kindling the torch of love and 

 rivalry on vasty breeding-grounds, is the prelude to these migra- 

 tions, is attested by travellers. A few white and blue butterflies 

 during July weather collect in this country at muddy spots, and 

 from some Alpine rivulet one may startle quite a bevy of thirsty 

 beings. But in tropical climates open spots by a river-side 

 become habitual diurnal resorts for vindictive males, who, 

 flecked in colour and innumerable in species, lend animation to 

 the watery whispers. Such spots form a natural parade-ground 

 for manifestations of rivalry, such as Mr. Wallace has noticed 

 displayed by the butterflies of Borneo, and form also a point of 

 departure for migration, which, regarded in this light, appears 

 intrinsically a modification of the aerial dance ; indeed, male 

 Lepidoptera are often noticed following one another when neither 

 migrating nor hurtling in the air — a fact often noticed, and that 

 has been put on record by the acute Edward Newman. " As 

 the waters retreated from the beach," writes Mr. Bates at 

 Obydos, on his voyage up the Amazons, "vast numbers of 

 sulphur-yellow and orange-coloured butterflies congregated on 

 the moist sand. The greater portion of them belonged to the 

 genus Callidri/as. They assembled in densely packed masses, 

 sometimes two or three yards in circumference, their wings all 

 held in an upright position, so that the beach looked as though 

 variegated with beds of crocuses. These yellow butterflies seem 

 to be migratory insects, and have large powers of dissemination. 

 During the last two days of our voyage (9th and 10th October) 

 the great numbers constantly passing over the river attracted 

 the attention of every one on board. They all crossed in one 

 direction, namely, from north to south,* and the processions 



* "Naturalist on the Amazons," p. 131. In Brazil, March, 1803, an im- 

 mense flight of butterflies of white and yellow col6ur continued for many days. 

 They were observed proceeding in a direction from north-west to south-east. 

 (Liudley, " Voyage to Brazil ;" ot Boyal Military Chronicle, March, 1815, p. 452.) 



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