MIGRATION AND DISPERSAL OF INSECTS : DIPTERA. 179 



the boat became perfectly black with insects. Attracted by the light 

 they flocked into the saloon, covering walls and ceiling in one dark 

 mass," &c. {Ent., vi., pp. 310-312). 



We may here observe that Van der Wulp records (Herkiots' 

 Bouwstojf'en, i., p. 140 (1853), that Chironomus Iw/iibris, Fries, 

 [z=occultan!i, Meig.), was to be seen by millions in March, 1852, in the 

 ditches near the railway-station (? at Leyden) where the neighbourhood 

 is generally under water in the winter, and in many places the water 

 was black with the abundance of these midges. They cannot fly, but 

 live on the surface of the water, over which they can glide with a 

 quivering motion of their wings as if sailing, and meantime, their 

 legs are stretched out motionless. From time to time they closely 

 shut their wings, a movement that covers the abdomen like a roof, 

 and then walk on the water just as another insect runs on a leaf. 

 Out of the water they begin a more rapid pace, and run like small 

 spiders swiftly in a circle very diflerent from other species of 

 ChiroyiomuR, which generally sit still, or walk forward slowly and 

 clumsily. In the same magazine {loc. cit., i., pp. 186-187 (1855)), 

 is the following notice from Rijwijk, which was published in the 

 Handehhdad of January 8th, 1855. Among the unusual phenomena of 

 the present winter may be mentioned the innumerable multitude of 

 black flies which have been found on the quay of the flooded land, 

 living on the surface of the water, and which were brought by the 

 south and southwest winds. They were not localised to a single 

 spot, but extended as far as the length of the quay (for more than a 

 quarter of an hour's walk), and, in several j)laces, were equal to a palm 

 in thickness. It was strange and wonderful to see them. The 

 midges were apparently Chironomus occidtana, Meig. { = lH(jubriH, Fries). 

 The preceding winter the same insect was found in innumerable 

 multitudes on the flooded meadows in the neighbourhood of the Hague, 

 and is probably always to be found in suitable localities in flooded 

 districts in mild winters. 



Sharp notes (Insects, ii., p. 505): "The species of the genus 

 Chlorops are famous for the curious habit of entering human habita- 

 tions in great swarms, many millions being frequently found in a 

 single apartment. Instances of this habit have been recorded both in 

 France and England, Cambridge being perhaps the place where the 

 phenomenon is most persistently exhibited. In the year 1831, an 

 enormous swarm of ('hlorojis Uneata was found in the Provost's Lodge 

 at King's College, and was recorded by Leonard Jenyns ; in 1870, 

 another swarm occurred in the same house if not in the same room. 

 Of late years such swarms have occurred in certain apartments in the 

 museums (which are not far from King's College) , and always in the same 

 apartments. No clue can be obtained whatever as to their origin ; 

 and the manner in which these flies are guided to a small area, in 

 numbers that must be seen to be believed, is most mysterious. These 

 swarms always occur in the autumn, and it has been suggested that 

 the individuals are seeking winter-quarters." Attention may here be 

 called to the peculiar swarming habit of Atlurix ibis when ovipositing. 

 For details see Ent., xxii., p. 193, pi. vii., figs. 1-2. 



Bearing on the question of the exportation of diptera into distant 

 countries is an interesting paper by Osten-Sacken [Trans. Ent. St,c. 

 Land., 1884, pp. 489 et seq.). He deals with the remarkable d'stri- 

 bution of Eristalis tenax, its sudden appearance over a great area in 



