MIGRATION AND DISPERSAL OF INSECTS; ORTIIOPTERA. 91 



of gravity, thousands being killed by the fall if it bo on stone or other 

 hard surface. If not interrupted by such causes they descend during 

 the afternoon." 



We have already referred to an irruption l)y night {(itttr, p. Go). 

 Newell reports that, in Iowa, a straw stack burning by night attracted 

 the locusts, and in the morning bushels of dead ones ' were found 

 in and around it. Aughey relates that whilst travelling at night on 

 the banks of the Bow River, in August, 18G6, a sudden change of wind 

 about midnight brought down " hosts of falling locusts," and that in the 

 morning they were found thick where none had been seen the night 

 before. A similar fall is reported as having occurred at 11 p.m. in 

 Nebraska, whilst many other observers report SAvarms as observed fly- 

 ing late in the evening. It is said that the young locusts that hatch 

 in the invaded region display gregarious instincts from the commence- 

 ment of their existence, congregate in immense numbers in warm and 

 sunny places, and during damp weather they seek the driest possible 

 positions. When migrating they move, as a rule, during the warmer 

 hours of the day, only feeding i"f hungry by the Avay, but generally 

 marching in a given direction until towards evening. They travel in 

 groups, in no particular direction, but purely in search of food, 

 although there is a general tendency for those hatching in the northern 

 states to go south, Avhilst those of the southern states generally tend to 

 go north. In 1875, near Lone, in Kansas, the young locusts crossed 

 the Potawotomic Creek, about 20-25 yards wide, in millions, whilst the 

 Big and Little Blues, two tributaries of the Missoiiri, one of which is 

 100 feet wide (the other rather less), were crossed at numerous places 

 by the moving armies which would march down to the water's edge 

 and commence jumping in, one upon another, and so pontoon the 

 stream to eft'ect a crossing. Riley further notes that a great army was 

 observed to fall over a perpendicular ledge of rock 25-80 feet in height, 

 passing over in a sheet apparently 6in.-7in. in thickness, and causing 

 a roaring noise similar to a cataract of water. 



Although there was evidence of a tendency for the early-developed 

 spring broods to leave the southern states in a north or north-westerly 

 direction, the actual result showed that those which reached into 

 north-west Dakota, Wyoming, and ^Montana Avere few in number, but 

 these return flights are small and unimportant, and are stated to have 

 " very little bearing on the general question except to show that even 

 with a superabundance of food they attempt to leave a country so 

 different from their native haunts, unfitted for their continued develop- 

 ment, in which they are infested by parasites and decimated by disease 

 in the course of a single generation." The information relating to these 

 " return " swarms is possibly the least satisfactory contained in the 

 lii'jxirt, and rests on so many probabilities that one hesitates to accept 

 a single generalisation. This is unfortunate, because it is this very 

 point, in which a migrating instinct is shown, that is most interesting, 

 and on Avhich the most exact and careful observations must be made 

 before generalisations can be indulged in. 



Supplementary reports were afterwards published, and in 1883 an 

 interesting report of the movements of M. sjinins in ^lontana in 1880 

 and in Wyoming, Montana, Ac, in 1881, was included in the TliinI 

 Report of tlic I'uitr'l States Comiiiif'sinn appointed to enquire into the 

 depredations of this and other insects. In this Itriioii, p. 21. Brunei- 



