1903] WEBSTER: — DIFFUSION OF INSECTS 55 



chian system does not approach the Gulf coast at its southern terminus, but leaves 

 a broad avenue that enables species moving eastward to pass on along the Gulf to 

 the Atlantic coast and thence northward. It does, however, to the northward form 

 an almost impassable obstruction to the directly westward migration of insects from 

 east to west, broken only in the State of New York and the country adjacent to the 

 north and south shores of Lake Erie. Here we have a huge gateway through 

 which nearly or quite all species imported from Europe, landing on our eastern 

 seacoast, north of the mouth of the Potomac River at least, make their way into 

 the comparatively level country beyond. Even the Atlantic Maritime brachypter- 

 ous Chinch-bug followed this trend. It is barely possible that the valley of the Big 

 Kanawha River in West Virginia and Cumberland Gap may offer passageways for 

 an occasional species, but of this we have no proof as yet. In the Cordilleran 

 system there do not appear to be any such openings or gaps for the influx 

 and diffusion of migrating species, except, perhaps, in extreme southern California 

 and Arizona, a country so arid that few species can take advantage thereof if it 

 really exists ; hence, a separation in South or Central America usually remains 

 permanent, while in the case of European species and the Appalachians, they 

 might easily make their way south along the Atlantic coast to the Gulf, and in a 

 comparatively short time mingle with the northern branch that has made its way 

 west to the great lakes and thence southward. 



A peculiar feature of the problem of introduced insects is that, although we 

 may have knowledge of their habits in their native homes, this is not always to be 

 taken as limitmg their actions in this country. The well-known household pest, 

 the carpet beetle, Anthretms scrop/iulariae, occurs along the Pacific coast, having 

 doubtless been introduced from Asia, but it does not there attack carpets. Soon 

 after it was introduced into the country along the Atlantic coast it began to destroy 

 carpets at a terrible rate, and it is now one of the most destructive of household 

 pests. I can well remember when it was unknown in Illinois, where now it does 

 much injury. In its native home it is a flower-frequenting insect, and I can always 

 find these beetles here in the United States in early spring in the blossoms of 

 tulips, more especially those of a white color. The allied species, Atithrenusrarhis, 

 also introduced, though a noted museum pest, is at about the same season to be 

 found frequenting the blossoms of the Spiraea. These illustrations go to show the 

 extreme flexibility of insects, not only in the matter of food but nearly every other 

 condition that enters into the problem- of their diffusion and development. 

 Generally speaking, insects are as plastic as clay in the hands of the potter, and we 

 need only to look to their immense numbers and variety to find proof of this. 

 They make their way over mountain, plain, and desert and are carried hither and 

 yon by the waters of rivers, lakes, and oceans, possibly to change their specific 



