No. 3.] DAWSON — THE LOCUST INVASION. 121 



tion a broad margin of uncertainty appears. It is probable, 

 however, that the great locust invasions are the resultants of the 

 actions of many agents, favorable or otherwise, all which it is 

 highly desirable should be known as a preliminary to methodical 

 and carefully devised efforts towards amelioration. 



The spring and summer of 1874 in the northern part of the 

 interior region were unusually dry, A dry climate is generally 

 supposed to be favourable to the locust, and chiefly to the greater 

 dampness of the eastern cultivated region is attributed the 

 deterioration in vitality of the insects produced in a following 

 year from eggs laid by an invading swarm. It is also noticed 

 that iu the eastern region the insect seldom survives to a third 

 year. Over the western breeding-grounds, therefore, a dry and 

 temperate spring may enable great numbers to come to maturity ; 

 while the continuance of the drought, combmed with the unusual 

 abundance of locusts, may tend to bring about wholesale emi- 

 gration. 



The locust has, however, many specific enemies, of which 

 Mr. Riley catalogues four. Trombidium sericium and Astoma 

 gryllaria are mites and external parasites ; Tachina anonyma 

 and Sarcojphaga carnaria, flies, the larvse of which feed on the 

 grasshopper and live within it. All these, or at least represen- 

 tatives of both classes, appeared with the locust swarms in 

 Manitoba in 1874, and the insects of some swarms appear to 

 have been weak and sickly from the number of parasites clinging 

 to them ; circumstances lessening to a considerable degree the 

 damage done by the insects, and the vitality of their eggs. The 

 quantity of locusts destroyed by birds, especially while the 

 insects are quite young, must be very great, and it has even been 

 suggested that the rapid succession of invasions during the last 

 few years may be due to the destruction-of game birds, especially 

 the prairie chicken. It would hardly seem, however, that this 

 is by itself sufficient cause, though it may be one among the 

 many. 



The position of Manitoba near the north-eastern limit of the 

 range of the locust, is in so far favourable, as it is only exposed 

 to invasions from directions included between west and south, 

 and the prevailing winds being north-westerly and coinci- 

 ding with the direction of the migration instinct of the insect, 

 carry the greater number of the swarms from their breeding 

 places to the South-Western States. The northern situation of 



