130 Brown : The Swarming of Collemhola. 



was noted in August, 1919, at Robin Hood's Bay, where on- 

 several large pieces of decaying sea-weed immense numbers 

 of Achoriites viaticus (Linn.) Tullb. were congregated ; so 

 densely were they crowded together that the surface of the 

 weed was completely hidden over several square inches, and 

 thousands of insects must have been present. 



In October, 191 8, Sminthiirinus aureus var. ochropus Reut. 

 was found in great numbers on an old stone wall at Bcauchief, 

 near Sheffield, and on October 24th, 1920, in the same locality, 

 many swarms of Achorutes purptirescens Lubb. were discovered. 

 In one particular case, several flat stones of a loose wall edging 

 a field were to a great extent covered. A rough count over 

 part of the surface gave approximately 200 insects to the 

 square inch, but in places, much of the stone was quite hidden 

 by clusters of individuals. The insects were either stationary, 

 or were wandering to and fro in an apparently aimless fashion. 

 The spot was visited the next day and also a week later, and 

 swarms were still in evidence. Still larger numbers of the 

 same species were found on November 6th, on a wall bounding 

 a garden near Dore, where for a distance of thirty yards or 

 more along the wall, crowds of individuals occurred, giving 

 the upper stones a distinct bluish -black tint. It is impossible 

 to give any estimate of the numbers present. Many of the 

 individuals were immature.* The explanation is not obvious. 

 There is no question of a possible migration here, as suggested 

 by Mr. Macnamara in the case of the decaying trunk mentioned 

 above, nor does the presence of a special food-supply seem 

 likely on a bare wall. Probably their ' home ' was in the 

 crevices of the loose wall, or somewhere on the garden side 

 in the last case, but why such numbers were apparently 

 airing themselves at the same time is difficult to explain. 



During the winter months, very large numbers of Ony- 

 chhirus armatus Tullb. and Dicyriomina viinuta O. Fabr. and 

 other winter species may be found on the under-side of fallen 

 trunks and similar places in woods, but in such cases there 

 is no suggestion of swarming such as has been described 

 above. 



: o 



Hull Museum Publication No. izi deals witli ' The Origin of the 

 Materials used in the Manufacture of Prehistoric Stone Weapons in East 

 Yorkshire,' is by Mr. T. Sheppard, and contains 46 illustrations of 

 implements. 



No. 86 of The Journal of the Quekell Microscopical Club contains 

 Hydrocarina : the Genus Eylais Latr.,' by C. D. Soar and W. William- 

 son ; ' A Log and some Mycetozoa,' by A. E. Hilton ; ' The Desmid 

 Flora of a Triassic District,' by G. T. Harris ; and ' The Microscopical 

 Structure of Lichens,' by R. Paulson — four excellent papers. 



* Laif^c minibers were again seen on the sanre wall on Decenilu'r ji^th. 



Naturalist 



