59 
flies observed by Zetterstedt which settled upon the carcase, 
not merely for rest, but for the purpose of oviposition, as that 
author himself suggests it (1). 
All observers know that the rat-tailed larvae of Hristalis 
ave not at all particular in the choice of the medium for their 
development; what they require is water with a sufficient 
amount of decomposing animal or vegetable matter in it. They 
occur in mire, particularly in fetid pools near stables, in ken- 
nels with a sediment of dirt, and other dirty places (‘aschen- 
berg, in Brehm’s Thierleben IV, p. 468). Frisch found rat-tailed 
larvae of Helophilus in similar places, in pools of dung-water and 
in other fetid liquids (Frisch IV, p. 26, Tab. 13). The larvae of 
Hristalis are amphibious and are often found creeping about 
dirty and musty places. Letzner (Schl. Ber. 1856, p. 117), who 
found two larvae in such a place and bred one of them, did 
not even know that its natural habit was aquatic; he says: 
,lebt an modrigen, staubigen Orten und an Hausern (also im 
Trockenen).“ Réaumur (IV, p. 440) says that he had often 
found rat-tailed larvae on dry land, long before he discovered, 
by a mere accident, a large number of them in the water. He 
says: ,1 had a glass-vessel emptied before me that contained 
water which I thought too fetid; many aquatic insects had pe- 
vished in this water, and many tree-leaves had become rotten 
in it; its bottom was filled with a black and offensively-smel- 
ap 0G ra I perceived that it was teeming with worms, 
easily recognisable as rat-tailed larvae. We obtained from this 
mud more than two-hundred specimens.“ At the same time 
(p. 443) Réaumur adds: he presence of such larvae in most 
offensively-smelling mud does not prove that such a medium is 
indispensable for them... I have found rat-tailed larvae which 
seemed to me of the same kind as the others in ordinary 
(1) That Réaumur does not mention ,the piping sound“, produced by the 
flies in flying, was probably because he took the fact for obvious, as Mristales 
generally produce that noise in flying (comp. on p. 20 the observation of the 
Japanese author). 
