THE DIFFUSION OF INSECTS IN NORTH AMERICA. Plate 2.^ 



BY F. M. WEBSTER, URBANA, ILL. 



The abundance and diversity of insect life during the warmer months are suf- 

 ficiently striking to attract the attention of even those not especially interested in 

 insects. To others of a more inquiring mind the questions arise as to the means 

 by which they came, and, being here, how it is that they are able to remain. It is 

 to the first proposition that this discussion will be directed. 



The careful observer of insect life will not fail to remark the gradual changes 

 that are constantly taking place in the insect fauna of any single area of country. 

 Some species, on account of changed conditions, due largely to the industries of 

 man, are disappearing, while others, before unknown, are, or seem to be, taking 

 their places. Probably there are few scientific men who have not, again and again, 

 had the question put to them in this way: "Is there a constant creation of new 

 insects going on, or are these we see only the old ones?" The question is easier 

 asked than answered, but I shall try to throw some light upon the somewhat obscure 

 problem by an arrangement of a portion of the data at present obtainable, and 

 which tend to throw light upon the subject not so much of insect creation, as of 

 insect diffusion. But at the outset I must call attention to the fact that this kind 

 of research can only follow on after considerable progress has been made in classi- 

 fication, and considerable knowledge obtained of the structure and habits of the 

 forms entering into the problems which we are to study. Again, as elsewhere in 

 the realms of zoological science, it sometimes occurs that affinities may appear in 

 the earlier stages of development and disappear entirely in the later stages. For 

 this reason we cannot even yet in many, perhaps the majority of cases, work out 

 our problems with a feeling of assurance that we have reached conclusions that 

 are final and may not, in the future, need revision. But no progress is made in any 

 science without effort, and some failures are inevitable, so that, generally speaking, 

 the best results are only such until some one else does better. 



Insect diffusion began in America a long way back in the obscure past, just 

 how far we do not know, but the remains of an ancient insect fauna have been pre- 



' Revised from a lecture delivered, February 1 1, 1903, at the University of Chicago. The map was drawn especially 

 for me by Dr. J. W. Folsom. 



