POSITION OF SWARMS 125 



there are a number of trees, and from the top of nearly every tree three or four 

 of the 'strange, smokclike columns could be seen standing up in the air, always 

 straight but not always vertical, some of them being inclined at small angles. 

 ... On watching one of the columns closely, it was apparent that all the gnats 

 liad their heads one way, facing the breeze, which, however, was a very light one. 

 It was a calm evening; what air-current there was came from the south-east. 

 It seemed to be sufficient occasionally to press back the column a few inches 

 from its normal position, and whenever this happened the whole body of gnats 

 jerked themselves forward again with one perfectly synchronous impulse.' 



" A picturesque account of a remarkable swarming of Culices, at Lewisham 

 Road near London, is given by Douglas. During ten days he observed ' the air 

 thick with millions of them, at times charging in close column up the road, like 

 a squadron of cavalry, at other times engaged in dancing up and down, after the 

 manner of their race.' These swarms were in evidence only during the hour 

 before dark and it appears were over or near the road, within reach of the 

 riding whips and sticks of the ' profatium vulgus.' Near by ' are several tall 

 trees, and round the top of the highest one only, at the same hour of the evening 

 that the periodical saltatory performances are going on in the road, enormous 

 swarms of gnats congregate. At first they appear as a small black cloud curling 

 about the ends of the branches, and soon, when the air is calm, rising in a close 

 column, like smoke from a chimney, for a distance of some 20 or 30 feet, the 

 bulk gradually becoming more grey and attenuated until lost to sight in the 

 upward progress. When a breeze is moving, the insects, always preserving close 

 order, are blown out laterally, and after skirmishing with the wind return to 

 their cover among the top leaves of the tree.' This last remark may be an as- 

 sumption and at such distance from the ground could hardly have been based 

 upon actual observation. Douglas suspects that the species in the tree was ' not 

 the same as that of the acrobats of the road,' and with right ; unfortunately 

 neither form was definitely identified. It further appears from the remarks of 

 Douglas that these swarms are an annual occurrence, only that the number of 

 individuals varies greatly from year to year. 



" In all the foregoing notes the writers failed to notice the true function of 

 these gatherings of Nemocera. However it had not escaped that keen observer 

 Gilbert White. He was evidently uncertain of the identity of the insects con- 

 cerned, for in his posthumously published notes he calls them ' empedes or 

 tipulce.' Speaking of their swarms at evening he says : ' At this juncture they 

 sport and copulate ; as it grows more dark they retire. All day they hide in the 

 hedges. As they rise in a cloud they appear like smoke.' No further mention 

 of copulation in connection with swarming appears until Taschenberg's popular 

 account of Gulex pipiens, published in 1883. He notes their habit of gathering 

 at the gables of houses and other prominences and describes how the females fly 

 to the swarm of males to effect copulation. In the notes on the swarming of 

 Chironomidge which follow, Taschenberg describes the formation over trees and 

 in tall columns, and we are left to infer that the Culex swarms do not assume the 

 columnar form — at least not in the same degree. 



" Radl has written two most interesting and suggestive papers on the light- 

 reactions of Arthropods and a great part of his discussion is based on the be- 

 havior of swarming insects, particularly of Culicids and Chironomids. It 

 would lead too far to enter into a discussion of these papers, but the fact is 

 brought out that these insects orient themselves towards some definite object 

 which is differentiated from its surroundings either by greater prominence or a 

 difference in color. He not only cites instances of orientation towards trees, 



