62 



DISTRIBUTION AND MIGRATIONS OF THE MORMON CRICKET 

 (ANABRUS SIMPLEX Hald.) IN COLORADO. 



By S. Arthur Johnson, Fort CoUiiis. Colo. 



During the past summer there was a serious outbreak of the Mor- 

 mon cricket in Colorado. The writer spent about two weeks in the 

 infested part of the State, where he collected many data and made 

 observations on the life history of this insect. It has been thought 

 best, in this account, to give, in the first place, a brief summary of 

 the facts obtained in each locality; second, to attempt to trace the 

 great waves of migration: and, third, to give a summary of this 

 information. 



Axiel, a town in Routt (\)unty, Colo., just north and east of the 

 Danforth Hills, was the nearest point we reached to what appears 

 to be the established home of A^iahnis simplex. A lady living on a 

 ranch 7 or 8 miles east of Axiel says that it is necessary to fight the 

 insects almost every year. The armies come in from the west and 

 travel east and up canyons. The migrations appear to begin soon 

 after the eggs have hatched and continue until Qgg laying begins 

 again, when the insects locate on the dry hills and devote their ener- 

 gies to pi'oviding for their oll's])riug. The pest is kept off the crops 

 here by herding or driving and making noises. 



At Hamilton, a town perhaps '10 miles east of Axiel, on the Wil- 

 liams Fork of Bear River, the migrations are less frequent, and we 

 were able to obtain definite data regarding them. The first observa- 

 tion was made by Mr. T. H. Hamilton and occurred in 1879. Nothing 

 more was seen of the insects until 1805, when a second migration is 

 recorded. Again, in 1900 and 1902, hordes of the insects passed 

 through. In these visits they took all kinds of garden and field 

 crops. Climbing the trees, they collected on the limbs until these 

 bowed with the weight of insect life. The migration from here in 

 each case was northeast. A glance at the map (fig. 6) will show that 

 the direction of their travel took them immediately into the Williams 

 River Mountains. To accomj^lish this they were obliged to cross 

 the Williams Fork, which flows with considerable speed at this place. 

 Immense nimibers were drowned in the attemjDt and floated down the 

 stream. In one case they came in contact with an obstruction and 

 formed a temj^orary dam to the water. According to the observa- 

 tions of Mr. Hamilton, the insects traveled about 30 miles in two 

 years. In each case when a brood has passed through, eggs haA^e 

 been laid in this locality. They hatch early in the spring as soon 

 as the snows melt (March or early April) . The young are not injured 

 by the rigors of the season. Frequently they are frozen stiff during 



