o6 . THE REPORT OF THE No. 19 



(Echlnospermnm Lappula). This was a new food plant for the species, and it is rather remarkable 

 that it should have been so conspicuously the favourite food plant in the West. The Blue Bur 

 is not indigenous on the prairies but has spread rapidly as an agricultural weed in Manitoba and 

 the North- West Territories during the past year or two. Upon some fields which had been left 

 for summer-fallowing large patches of this weed could be found stripped bare of every leaf by 

 the caterpillars of the Painted Lady. Other plants noticed in different places, which were eaten 

 by this caterpillar, were the Western Mugwort (Artemisia Ludovkiana) and the Pearly Ever- 

 lasting (A)iaphalis Margaritacea). In a few instances, caterpillars were seen upon the small 

 Round-leaved Mallow, and were reported on holyhock and burdock. At Kaslo, B.C., I was 

 surprised to find the laxvm feeding on the prickly Borraginaceous plant, Amsinckia 



intermedia. 



It is probable that our Canadian swarm may have come from the south and west. Mr. J. 

 W. Cockle, of Kaslo, on Kootenay Lake, B. C, an energetic and very observant entomologist, 

 wrote me last spring that on May 2nd a swarm of this butterfly had passed Kaslo. He says : 

 " They were here on that date in thousands, but most of them only stayed a day or two ; from 

 which I suppose they have migrated to some other point." At the same time Mr. Cockle sent 

 me the following inteiesting extract from the Spokane Review of May 26th : 



MIGRATION OF BUTTERFLIES. 



Spokane Review, May 26. 

 Countless Thousands ok them flyinc over Southern U.vlikornia. 

 " For weeks a remarkable migration has been taking place in southern California, and is still 

 in progress. The migrant is a brown butterfly, known as Pyrameis cardui. 



"At first the butterflies were noticed in twos and threes, then in dozens, then in countless 

 thousands, all flying in one direction, to the northeast and parallel to the Sierra Madre range, 

 Some idea of the numbers can be conceived when it is said that in looking across a lawn 90x40 

 feet four or five butterflies were continually crossing the line of vision, and this was true, so far 

 a9 could be learned, of every lot in the vicinity. 



The insects move with a regular rate of speed, always in the same direction ; now in pairs, 

 again singly or in groups of 10 to 12. Such specimens examined show that they had trave led a 

 long distance, and it is thought by some that the migration began in Mexico, hundreds of miles 

 away. 



In attempting to guess at the cause, it may be assumed that it has been a favorable year for 

 this butterfly in some region to the south, and thaf the countless caterpillars have changed into, 

 butterflies in such swarms that to obtain food they have begun this migration, the direction of 

 -which has been governed to some extent by the mountain range." 



It may be the case that after this year P. Cardui will be less abundant than usual for some 

 years, in accordance with the rule which seems to govern the occurrence of insects in general, 

 namely, that an excessive abundance of a species generally foretells an unusual scarcity the next 

 or the following year. Any remarkable observation concerning insects should always set the 

 careful observer thinking, so that, if possible, the cause for the unusual occurrence may be dis- 

 covered. 



At the end of Dr. Scudder's article he gives the following under the head of Desiderata : 

 "Cardui is one of the best subjects of study for those who wish to investigate the causes of 

 irregular apparition ; and only those who spend much time in the field can hope to solve the 

 problem. A close observation of the comparative abundance of the butterfly for several con- 

 secutive years in the same locality, accompanied by the attempt to rear hundreds of the cater- 

 pillars, selecting only those which are very nearly full grown, and recording the proportion of 

 healthy and infested ones, will probably show whether the attack of parasites is a vera causa. 



