DIPTERA. 47 



living ribbon be brought into contact with the anterior, a circle is 

 formed, which turns round and round on the same ground for a long 

 time, sometimes even for a whole day, before breaking, and continu- 

 ing to advance. They are never met with in bad weather, but only 

 when the sun is warm. 



The curious and astonishing phenomenon of an assembly of 

 larvae without feet, advancing with an equal movement resulting from 

 the individual motion of thousands of little worms, was remarked for 

 the first time, in 1603, by Gaspard Schwenefelt. This naturalist says 

 that the inhabitants of Siberia consider this phenomenon as an indi- 

 cation of a bad harvest if they go towards the mountains ; whereas, 

 if they descend towards the plains, it is the sign of a good one. In 

 1715 Jonas Ramus mentioned the same phenomenon, recalling a 

 superstition attached to it by the peasants of Norway. This writer 

 informs us that the peasants of that country, on meeting one of these 

 moving columns, throw down their belts or waistcoats on the ground 

 before it. If the orme-drag (that is the name given to the moving 

 column) crosses over this obstacle, it is a good sign ; but on the other 

 hand, if the column turns round the obstacle, instead of crossing it, 

 some mischief may be expected. 



The same animals were observed in 1845 at Birkenmore, near 

 Hefeld, by M. Rande, Royal Inspector of the Forests of Hanover. 



M. Guerin-Meneville is of opinion that these larvae, which exist 

 in great numbers in certain districts, sometimes devour all the nutri- 

 tive substances contained in the ground. After having done so, 

 they are obliged to come out of it, in order to seek at a distance a 

 place where they will find food, or perhaps only a suitable place to 

 undergo their metamorphosis. It is then that this singular journey 

 commences. As regards the uniting of these myriads of individuals 

 into columns, M. Guerin-Meneville thinks that it can be explained 

 by the necessity these insects feel for mutual protection against the 

 drying effect of the atmosphere when they are forced to leave the 

 ground. United into masses, and moistened by the glutinous matter 

 which connects them, they can leave their former place of abode 

 without danger j if each were by itself, they would soon perish. 

 Here, as in other cases, union is strength ; and the strength of these 

 larvae lies in this protecting moisture. However it may be explained, 

 the migration of these troops of insects are among the most astonish- 

 ing phenomena of Nature. 



BRACHYCERA. 

 The Brachycera, from fyaxvs, " short ;" and Ktpas, " a horn " 



