22 CATALOGUE OF BriTEKFLIES. 



is said to be world-wide. Large swarms of it are sometimes 

 observed, but perhaps that of 1879 was the most extraordinary. 



In that year an immense flight of this species apparently took 

 its rise in [N'orth Africa, crossed, first the Mediterranean, and 

 then the entire Continent of Europe, enormous numbers reaching 

 Britain early in June. A full account of this most unusual 

 occurrence will be found in an article in the Entomologist Maga- 

 zine, vol. xvi., old series, p. 49, in which the insect is traced 

 from JSTorth Africa, where it was noticed about the middle of 

 April, through Spain, Italy, Switzerland, Austria, France, etc. 

 'NesLY Geneva '^ the swarm is said to have obscured the sun for 

 several minutes." At Angers it was estimated that 40,000 to 

 50,000 passed along a single street in an hour. At Steyer, in 

 upper Austria, on the 11th June, it was "estimated at above 

 rather than below 1,000,000." The general direction of flight 

 seemed to be from south to north, and after its arrival here it 

 appeared to spread quickly over the whole island and was abun- 

 dant in these counties. 



In other years it has been equally common. Then it will 

 disappear altogether for some time, or appear in very small 

 numbers. Yarious theories have been put forw^d to explain 

 the phenomenon, but a lengthy discussion would be out of place 

 in a catalogue. My opinion is that Cardui is a double-brooded 

 species, and that the larvse of the second brood often perish in 

 our early winter. I have found the larvae myself at Hartlepool 

 in November, but was unable to obtain Butterflies from them. 

 These autumn larvae have, however, been reared indoors, but 

 those exposed to the weather must all have perished. Thus, 

 after a large immigration, we find the larva abundant in July, 

 and the Butterfly in August, but these fail to perpetuate their 

 race here. The species is recorded in all the lists in my posses- 

 sion, but it is unnecessary to give particular localities for a 

 species that occurs everywhere, when it appears at all. 



