The Syrphus Flies 



"rat-tailed maggots" and are very curious objects which are 

 frequently sent to entomologists for name. 



Those which live in ants' nests belong to the genus Microdon 

 and are among the strangest insect larvae known. They do not 

 look like insect larvae, and, in fact, resemble certain land shells. 

 Curiously enough, they have been described and named as species 

 of mollusks. In fact, certain insects have given shell students a 

 good deal of trouble, for, as will be shown when we study the 

 caddis-flies, certain cases constructed by these insects have also 

 been described as shells. The Microdon larva does not appear to 

 be jointed and the upper surface of its body is covered with a net- 

 work of bristles which usually hold a coating of dirt. There is 

 no trace of any head and the sides of the body project, forming 

 a sort of fringe around the edge. The soft pupa is formed within 

 the last larval skin and does not alter its shape. Just what these 

 larvae do in the ants' nests is not well understood. Perhaps the 

 ants gain some secretion from them. As a matter of fact they 

 are sometimes found elsewhere. The adult flies of this genus are 

 usually dull-colored, are slow fliers and are 

 found on the borders of low-growing 

 woods. The flies have been seen laying 

 their eggs in the ant hills and the ants have 

 Fig. 84. Rat-tailed been seen to drive them away but they re- 

 turned again, undiscouraged by the im- 

 polite rebuff. This fact would not seem 

 to indicate that the larvae are of any service to the ants. 



Those syrphus flies which live, in their early stages, in the 

 nests of bumblebees belong to the genus Volucella, and the flies 

 of this genus rather closely resemble bumblebees. Their larvae 

 were for a long time considered to be parasitic upon the young 

 of the bumblebees but later observations have practically dis- 

 proved this and we are forced to conclude that the Volucella larvae 

 are simply scavengers, feeding upon the waste or excreta of the 

 bee larvae and even upon the dead bodies of those which die. 

 The bumblebees seem to realize that the syrphus flies are not 

 inimical to them, since they allow them free access to their nests 

 and do not seem in the least disturbed by their presence. 



The most famous of all the syrphus flies is the one which 

 commonly goes by the name of the drone fly. It is Eristalis tenax 

 and its larva is one of the rat-tailed maggots. It is a cosmo^ 



