importation or non-importation of Diptera. 491 



fly in Georgia, Missouri, Illinois, and even on the 

 Pacific coast. 



The other possible hypothesis is that Eristalis tenax, 

 like some other European species (for instance, Sijrphiis 

 'pijrastri), was indigenous on the western side of the 

 American Continent only, and not on the eastern ; and 

 that it began to spread eastward since civilization in its 

 westward progress came in contact with the area of its 

 occurrence. The Colorado-beetle reached the Atlantic in 

 that way, and^l. Fulleri is another remarkable instance. 

 Dr. Horn says (Bull. Brooklyn Ent. Soc, No. 6, 1884) :— 

 " In 1874, when working with Dr. Leconte on the 

 Rhynchophora, among all his material only a single 

 specimen of Aramigcs Fulleri was contained, and that 

 came from Montana. A year or two later it was received 

 from all parts of the country, and was dreaded as one of 

 the worst hot-house pests. How did this species spread 

 so suddenly over so large a territory ? Prof. Lintner 

 had first found the insect in 1876. Mr. Dimmock finds 

 it very troublesome in hot-houses, particularly on roses." 

 E. tenax may have reached Missouri and Illinois years 

 ago without being noticed ; it attracted attention as soon 

 as it appeared on the Atlantic coast, where dipterologists 

 could recognise it. This supposition is supported by the 

 fact that E. tenax exists in Siberia and Japan ; but it is 

 somewhat weakened by the circumstance that, as far as 

 I know, it has never been found in California. I have 

 been collecting seven months in California, in 1876, and 

 have carefully examined the collection of Henry Edwards, 

 Esq., in San Francisco, without seeing a single specimen 

 of that species. However that may be, the suddenness 

 of the appearance of E. tenax on the Atlantic coast of 

 North America is a very extraordinary fact ; and if im- 

 ported from Europe, this fly is a noteworthy instance of 

 an importation after nearly four centuries of intercourse. 



2. — Sarcophaga carnaria. 



Importation, after all, is not such a very easy matter 

 as it would seem. It took four centuries to import 

 Eristalis tenax into America (if it was imported at all), 

 a very common species spread all over the Old World, 

 and which owes its very name to the remarkable powers 

 of endurance of its larvae. I will give now an instance 

 of an equally common and equally enduring European 



