304 THE CAUSES WHICH 



gigantic flights of the same species were observed in Turin and 

 other places. According to the report presented by Professor 

 Eimer^ of the University of Tiibingen, on the swarms of the 

 present year, the first notice of these massive hosts of butterflies 

 was made at Turin on June 1st ; next in Switzerland, from 

 June 2nd to 9th ; then in Alsace, France, and Spain, from June 

 5th to 10th j and latest in Wiirtemberg, from June 11th to 

 21st. As a result of his anatomical observations, Dr. Eimer 

 found that eighteen out of every nineteen of these troops were 

 females who were all laden with eggs, and he believes that the 

 object of the great emigration was the discovery of a home in 

 which to deposit them. They seem in the first instance to have 

 been wafted to us from Africa, the swarm traversing Algiers in 

 a north-easterly direction as early as from the 15th to the 20th of 

 April, and reaching Valencia and Italy in about ten or eleven days.'" 

 Next to Tyrameis cardul, Danais Archijipus has a wide 

 distribution. It occurs in the New World from Canada to 

 Bolivia, and has spread over some of the islands of the Pacific 

 to Queensland and New Guinea. According to Mr. Riley, these 

 butterflies hibernate through the winter, and then often appear 

 in immense swarms. In September, ISOS, accounts were received 

 of their sudden appearance in difl:erent parts of the city of 

 Madison, Wisconsin, and at Manteno, 111. ; whilst on the 19th 

 of that month at St. Joseph, INIo., millions of them were seen 

 filling the air to the height of three or four hundred feet for 

 several hours, flying from north to south. And again in the 

 spring of 1870 a remarkable swarm was seen at Manhattan 

 about the middle of April,"^ which, as reported by a resident of 

 that place, came rapidly with a strong wind from the north-west 

 and filled the atmosphere all around for more than an hour, 

 sometimes so as to eclipse the light. The handsome black and 

 green Swallow-tailed, Urania leilus and Marius, which from 

 their larval forms are sometimes affiliated to the large-bodied 

 moths, migrate periodically from Orizaba in Mexico along the 

 foot of the Cordillera Mountains to Rio Grande in Texas. On 

 the wing alone during the prime of the morning hours their 

 passage occupies from three to four weeks, and then at the 

 expiration of from five to six the cohorts retrograde, much deci- 

 * W. L. Distant, Trans. Ent. Soc, 1877, p. 93. 



