2i8 NATURAL HISTORY OF AQUATIC INSECTS 



Eristalis hovering about the carcass of a sheep which 

 was immersed in putrid liquid. 



The habits of EristaHs tend to bring it about the 

 habitations of man. Hence it is not altogether sur- 

 prising to learn that it employs the facilities afforded 

 by steamers and the like to increase its range. Like 

 the pig, and still more like the rat and the cockroach, 

 it bids fair to follow traders over the whole world. 

 Baron Osten Sacken, whose unrivalled knowledge of 

 Diptera makes his testimony conclusive, gives the 

 following particulars as to its immigration into fresh 

 countries. 



Before 1875 Eristalis tenax was only known to occur 

 in the temperate regions of the old world. During 

 twenty years of residence in North America Osten 

 Sacken never met with a specimen until on Nov. 5, 

 1875, he found one on a window at Cambridge, Mass. 

 Next year he observed several specimens at Newport, 

 R.I. The species has now completely overrun the 

 United States, and has occurred in Canada. The in- 

 vasion proceeded not from E. to W., as might have 

 been expected, but from W. to E. Eristalis tenax 

 has also been found in New Zealand, but not as yet 

 in Australia.^ 



Note. — An account of the aquatic larva and pupa 

 of Pericoma (see pp. 92, 160), by L. C. Miall and N. 

 Walker, will appear in Trans. Entom. Soc, 1895. 



1 Details are given in Baron Osten Sacken's Oxen-born Bees. 



