Januaey 17, 1913] 



SCIENCE 



87 



In the year 1911 but little could be done on 

 this subject; but beginning with April of the 

 present year a continuous program of observa- 

 tions, collections and breeding-cage studies 

 has been steadily maintained and is still in 

 progress on the Illinois River, and a careful 

 survey has been made of the surroundings of 

 the six insane hospitals of the state, and of 

 the almshouse of the county in which the city 

 of Chicago is situated. Cases of pellagra 

 have occurred in all these institutions during 

 the above-mentioned period, but in widely dif- 

 ferent ratios to the total number of inmates 

 in each — ^the Peoria asylum, for example, con- 

 taining, in 1909, twelve times as many cases 

 per thousand inmates as did any other insti- 

 tution in the state. It thus became a matter 

 of special interest to know the facts in detail 

 concerning the occurrence and abundance of 

 SimuUum in the immediate neighborhood and 

 in the general vicinity of all these institu- 

 tions. 



Besides this work in the field, the insect 

 collections of my office for many years have 

 been carefully examined, and its field notes 

 and accessions records have been sifted for 

 evidence bearing on the species and distribu- 

 tion of Simulium in the state at large ; and the 

 whole body of the American literature of the 

 subject has been critically studied, with some 

 reference also to a considerable list of Euro- 

 pean articles. 



According to the present state of our knowl- 

 edge there are approximately seventy species 

 of Simulium on record for the whole world, 

 of which we are known to have but fifteen in 

 the United States of North America. Nine 

 species, or possibly ten — the status of one be- 

 ing uncertain — have been found in Illinois, 

 one of which, 8. hirtipes, occurs also in 

 Europe. No other European species has been 

 found on the continent of North America, 

 although 8. repians is reported from Green- 

 land. The slight attention hitherto paid to 

 these insects in America is illustrated by the 

 fact that two of our nine Illinois species — or 

 three of them, if there are ten in the state — 

 are new to science, descriptions of the two 



known to be new being now in press, under 

 the names of venustoides and johannseni? 



As the state of Illinois extends, from north 

 to south, through five and a half degrees of 

 latitude, there is some difference between its 

 most northern and its most southern districts 

 in respect to the predominant species of 

 8imulium; but as all have similar habits, and 

 all but one of them are active biters, this fact 

 probably counts for little in the present dis- 

 cussion. 



There is some difference also as to the kinds 

 of waters in which the several species prefer 

 to breed, some of them living mainly in the 

 larger rivers, and others occurring only in the 

 smaller streams; but as the state is well wa- 

 tered in all its parts, and is virtually a level 

 plain, there is no part of it which is wholly 

 beyond the reach of some species of Simulium. 

 It is true that these insects are rarely seen in 

 some places, and are an annoying nuisance, 

 and indeed a destructive pest in others, espe- 

 cially along the larger rivers in spring; but 

 since we have found them in considerable 

 numbers at a distance of more than five Eng- 

 lish miles from the nearest water in which 

 they could have bred, and since there is 

 scarcely a small stream anywhere in some 

 part of which Simulum larvae can not be 

 found throughout the spring and summer, 

 even temporary roadside drainage ditches 

 often containing them during the spring sea- 

 son of high water, there must be few people in 

 the state who are not at some time exposed 

 to the attacks of the flies. Simulium is, in 

 fact, more completely and uniformly distrib- 

 uted in Illinois than Anopheles, and as there 

 is no part of the state wholly and permanently 

 free from malarial disease, there would seem 

 to be no part of it free from danger of pel- 

 lagra, if this is really transmitted by black- 

 flies. 



The contrast is marked between these Illi- 

 nois conditions and those in Italy, where Sam- 

 bon and his colleagues studied the problem of 

 pellagra and the distribution of the black-fly. 



- Since printed in a reprint from the 27tli Eeport 

 of the State Entomologist of Illinois, pp. 32 and 

 42. 



