ECOLOGY OF ISLE ROYALE. 313 



to Europe and North America. Widely distributed in northern North 

 America from Ne^v England to British Columbia and Alaska. 



24. Platy.cliirus hi/pcrhorevs Staeger. Taken at Light-house clear- 

 ing (I, 7) July 23 and 26. Type locality Greenland but widely dis- 

 tributed in North America. As with most species of the genus only 

 the males can be identified satisfactorily by the known characters. 



25. Ilelmwstoma angustatum Williston. Specimens taken July 2-3 

 and 26, at Light-house clearing (I, 7). Type locality, state of Wash- 

 ington. Known also from the White Mountains and British Columbia. 



26. Slfrphus americamis Wiedemann. One specimen taken July 22, 

 at Light-house clearing (I, 7). The species is abundant and somewhat 

 variable in coloration and is distributed over nearly the whole United 

 States and Canada. The larvae have been observed feeding on the grain 

 Aphis. 



27. Syrphus dicersipes Macquart. Specimens taken August 4 and 

 7, (V, 3). Type locality Newfoundland. Distributed from New York 

 to British Columbia and Alaska, reaching as far south as southern Ohio. 



28. Syrphus genualis Williston. Taken July 24, at Light-house 

 clearing (I, 7), July 25, (II, 1). Type locality New Hampshire and 

 recently reported from Beulah, New Mexico. 



29. Syrphus ribesil Linn. Specimens taken July 24 and 26 at Light- 

 house clearing (T, 7). Common to Europe and North America. This 

 is one of the most common members of the family and is almost sure to 

 be included in local lists of Diptera as it is distributed over nearly the 

 whole of North America. The larvae are of importance as they feed on 

 various species of plant lice. One often sees a colony of plant lice with 

 one of the syrphid larvae in the midst of them, and he cannot help be- 

 coming interested if he observes for a short time and endeavors to count 

 the number of plant lice a larva is able to devour in a given time under 

 favorable conditions. 



30. Sphaerophoria cylinilrica Say. Specimens taken July 25, 26, and 

 28 at Light-house clearing (I, 7) and July 25, (II, 1). Type locality 

 Pennsylvania. Common over a wide range and included in many local 

 lists. The larvae are reported as feeding on the grain Aphis and on that 

 account the species is of interest to the economic entomologist. The 

 sexes are quite different from one another and one is not likely to asso- 

 ciate them on first acquaintance. 



31. Eristalis dimidiatus Wiedemann. Specimens taken July 22, 24, 

 25 and 26 at Light-house clearing (I, 7), August 4 (V, 3) and July 25 

 (II, 1). About 40 specimens of this species were procured indicating 

 that it is as common at Isle Royale as at other places. The larvae of 

 the various species of Eristalis are what are known as rat-tailed larvae 

 and are found in shallow water in swampy places or at the outlet of 

 sewers and drains. Each larva 'is furnished with a posterior appendage 

 which can be lengthened and shortened at will and which contains the 

 posterior parts of the tracheal trunks. At the free end of the appendage 

 are the two posterior spiracles which are kept at the surface of 

 the water. Thus the laiwa is fitted so it can remain beneath the water 

 and yet get the necessary air for cari'ying on respiration. The adults 

 are common around flowers in autumn, sometimes several species visit- 

 ing the same patch of asters or goldenrods as the case may be. E. dinii- 



41 



