﻿160 SEVENTH ANNUAL REPORT 



Elm and Oak, were either untouched or but little injured, while the 

 following trees were preferred in the order of their naming : Ash, 

 Willow, Cottonwood, Balm of Gilead, Silver-leaved and Lombardy 

 poplars, Black Ash, Black Locust, Black Walnut, Hickory, Ailanthus, 

 Maple, Sumach and Evergeens. 



In every case they show a marked preference for plants that are 

 unhealthy or wilted. 



TIME OF APPEARANCE. 



In endeavoring to deduce some general conclusions respecting 

 the time of year that the 187-1 swarms reached difierent parts of the 

 country, great difficulty is experienced in sifting those accounts which 

 refer to the progeny of the 1873 invasion, and the new comers which 

 hatched within the insect's native range. Yet we shall find, as a rule, 

 that the insects which hatch outside the native habitat — i. e., in Min- 

 nesota, Iowa, Missouri, and the larger part of Nebraska and Kansas — 

 acquire wings and leave before the new swarms appear. In the more 

 northerly of the States, as in Minnesota, the insects hatched on the 

 ground acquire wings in June, and earlier in proportion as we go 

 south, until in Texas they become Hedged in April. The time of 

 appearance of the new swarms is in inverse ratio ; i. e., earlier in the 

 more northern, later in the more southern States. Thus, while on the 

 confines of the insect's native habitat, it is almost if not quite impos- 

 sible to distinguish between the old and the new comers, in respect 

 to the time of their acquiring wings ; the difference in this respect 

 becomes greater the farther south and east we go. The 1874 swarms 

 appeared during June in Southern Dakota, during July in Colorado, 

 Nebraska and Minnesota ; during the latter part of this month in 

 Iowa and Western Kansas. During August, they came into Southeast 

 Kansas and Missouri ; and by the middle of October they reached 

 Dallas, in Texas. 



One noticeable feature of the invasion was the greater rapidity 

 with which the insects spread in the earlier part of the season, while 

 in fullest vigor, and the reduction in the average rate of progress the 

 farther east and south they went. The length of their stay depends 

 much on circumstances. Early in the Summer, when they first began 

 to pour down on the more fertile country, they seldom remained more 

 than two or three days, whereas, later in the season, they stayed much 

 longer. In speaking of the advent and departure of these insects, I 

 use relative language only. The first comers, when — after having 

 devoured everything palatable — they take wing away, almost always 



