6 Mr. R. Patterson on the appearance of Clouds of Diptera. 



III. — Note on the appearance of Clouds of Diptera. By 

 Robert Patterson, Esq., Member of the Nat. Hist. Soc. 

 Belfast, &c. 



The appearance of Dipterous insects in large numbers is in 

 certain localities and at certain times a matter of common ob- 

 servation. About Lough Neagh myriads of Culicida, Tipulidce 

 and Ephemerida are seen, and Culex detritus is recorded by 

 Mr. Haliday* as rising above trees, so as to resemble the smoke 

 of a cottage chimney. In Phil. Trans. 1767 5 it is stated that 

 in 1736 the common gnat {Culex pipiens) rose in the air from 

 Salisbury Cathedral in columns so resembling smoke, that 

 many people thought the cathedral was on fire. In Norwich, 

 in 1813, a similar alarm was created. At Oxford, in 1766, " a 

 little before sunset, six columns of them were observed to as- 

 cend from the boughs of an apple-tree, some in a perpendi- 

 cular and others in an oblique direction, to the height of fifty 

 or sixty feet ff 



A phenomenon similar to that last mentioned was this 

 summer observed for some days at Belfast. Wherever there 

 were trees, columns of insects were seen, and attracted the 

 notice of even the most incurious. They began to appear a 

 little before seven o'clock, and diminished in numbers as the 

 light decreased, so that by half-past nine few were visible. 

 On the evening of June the 1 1th, I went with Messrs. Bryce 

 and Hyndman to the house of our fellow-member Mr. Grattan, 

 situated on the north side of the bay, and about half a mile 

 from the town, for the purpose of observing them. The fol- 

 lowing notes were there drawn up, our remarks being limited 

 to an irregular semicircular area, having an average diameter 

 of seventy or eighty perches. 



The insects appeared in columns above the trees, the shade 

 of colour varying according to the greater or less density of 

 the mass from that of light vapour to black smoke, the co- 

 lumns not only differing in this respect from each other, but 

 each column being frequently different in different parts. They 

 might have been mistaken for dark smoke-wreaths but for 

 their general uniformity of breadth, and for a graceful and 

 easy undulation, similar to that of the tail of a boy's kite, 

 when at some height and tolerably steady. The individual 

 insects flew about in each column in a confused and whirling 

 multitude, without presenting in their mazy dance, any of 

 those regular figures which gnats frequently exhibit over pools 

 of water. The motion of their wings filled the air with a pe- 



* Entom. Mag., No. 11. p. 51. t Kirby and Spence, vol. i. p. 1 14. 



