DIPTERA. 51 
accord, leaving a track after it on the ground, as a material in- 
dication of its presence. 
These strange collections of living creatures form societies, 
sometimes only a few yards long; but at other times it hap- 
pens that they form bands from ten to twelve yards in length, 
of the breadth of a hand and the thickness of a thumb. M. 
Guérin-Méneville observed columns as many as thirty yards in 
length. These troops advance as slowly asa snail, and in a certain 
direction. If they encounter an obstacle—as a stone, for instance 
—they cross over it, turn round it, or else divide into two 
sections, which reunite after the obstacle is passed. If a portion of 
the column be removed so as to divide it into two parts, it is 
quickly re-united, as the hindmost portion soon joins that which 
precedes it. Lastly, if the posterior part of this 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, some- 
times even for a whole day, before breaking, and continuing 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 
larvee without feet, advancing with an equal movement result- 
ing 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 indication of a bad harvest if they go to- 
wards the mountains; whereas, if they descend towards the plains, 
it is a sign of a good one. In 1715 Jonas Ramus mentioned the 
same phenemenon, 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 Birkenmoor, 
near Hefeld, by M. Rande, Royal Inspector of the Forests of 
Hanover. ° 
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