2 
96 AN ACCOUNT OF BRITISH FLIES. 
the alimentary canal being plainly seen through the integuments. 
On the ventral surface organs of locomotion seem to be represented 
by slight swellings armed with bristles. 
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Fic. 14.—A. Larva of Sciophila ; B. Larva of Ceroplatus ; c. of Sciara. 
The habits of the larvee are interesting. They are all gregarious. 
They all, with the exception of Scéava, seem to live in fungi. Sciara 
prefers vegetable mould and under the bark of trees for its home. 
The larvee, according to various observations, appear to moult several 
times before they pupate. The Sciophila larve do not live. inside 
fungi, but seem to prefer to crawl about on the outer surface, on the 
under side of the pileus, which they cover with threads. This web- 
formation is a very common feature in the larve of this family ; a 
coarse webbing is formed over the surface or under side of the pileus, 
and in and under this the larve live. The larve forms a slimy 
tract where it crawls along. Perhaps the most interesting are those 
of Sciara, known as the “Army Worm.”* They differ from other 
Mycetid larvee by the absence of any bristles on the ventral surface, 
by the structure of their trophi and by their habits, nearly all living 
in large numbers under the bark of trees and in mould. At certain 
times these larvee seem to migrate, for what purpose we do not know. 
They form columns twelve to fourteen feet in length, two or three 
inches broad and half an inch thick, containing countless numbers 
as close together as they can be packed. These processions are often 
seen in woods on the Continent, but what they are for or what they 
mean we cannot tell ; as the larvze are always full grown it cannot be 
for feeding purposes. It is this habit that has given them the name 
of “Army Worms.” Some larve of this family are noted for a 
* Heer-wurm is a better term, as so many larve which are gregarious are called 
«¢ Army Worms.” 
