FOREWORD 
pa ecst a century ago, Benjamin D. 
Walsh, the first State Entomologist of 
Illinois, became interested in the mayflies or 
shadflies of the area about his home in Rock 
Island. Since his first observations and writ- 
ings concerning these insects, a great deal has 
happened to the Illinois environment, and 
great advances have been made in our knowl- 
edge of this interesting part of our native 
fauna. The following treatise by Dr. B. D. 
Burks, formerly of the Natural History Sur- 
vey, brings our knowledge of this group up 
to date. 
Mayflies are of importance to people in 
many ways. One of the most obvious is the 
swarming and massing of some species in 
such strategic places as river bridges, where 
at times the bodies of countless millions form 
barriers or hazards to trafic. But these 
dramatic occurrences are far from the most 
important aspects of the lives of mayflies. 
As a part of the biological complex of our 
waters, for all mayflies are aquatic in their 
developmental stages, these insects find their 
most important place in human economy and 
interest. They are an important link in con- 
verting microscopic food organisms and veg- 
etable detritus into units large enough and of 
proper character to be of value to our pred- 
atory fishes. This fact has been employed 
by fly tiers in the design of certain artificial 
lures intended to be attractive to certain fishes. 
Furthermore, mayflies may be characteristic 
of certain types of waters. Dr. Burks has 
listed a dozen different habitats, with species 
typical of each. This association of insect 
with habitat is of importance to all workers 
interested in our fresh waters, as the mayfly 
species which are present in a given body of 
water may indicate the condition of that 
water and therefore its usefulness for domes- 
tic or industrial purposes. When Walsh 
studied the mayfly populations in the Rock 
Island area, he found a considerably different 
species complex from that existing in the area 
now. In spite of much careful collecting in 
the Rock Island vicinity, Dr. Burks could re- 
cover only 8 of the 31 species which Walsh 
recorded from there. ‘This recovery repre- 
sents only about 26 per cent of the mayfly 
fauna present before the damming, dredging, 
siltation, and addition of pollutants which 
characterize these waters now. It was neces- 
sary to extend the search into less modified 
waters in order to rediscover some of the 
other species with which Walsh was familiar. 
And then there is the peculiarness, the 
uniqueness, of this archaic group of insects, 
of interest to all who profess a delight in 
nature. In this group, as seldom found in 
an aggregation of related animals, there is a 
great divergence from that which we consider 
to be the accepted pattern. ‘The morphology 
of mayflies is reminiscent of the morphology 
of insects which disappeared many millions of 
years ago and which are now known only 
through fossil remains. The adult stage has 
become a mere vestige, lasting usually but a 
very few days at the most. The life span is 
consumed almost entirely by the developmental 
stages under water. All of the eating is done 
during this growth period; the adults have 
useless mouthparts and digestive systems. Of 
all of the winged insects, mayflies are the 
only ones which shed their skins after they 
have developed wings with which they can 
fly. And a few species reproduce their kind 
without ever attaining the true adult stage! 
Thus, we find that mayflies are important 
not alone to harassed highway maintenance 
men and press photographers. They are 
much more so to those entrusted with the 
well-being of our fish populations, those in- 
terested in the public health and other values 
in inland waters, and those interested in the 
peculiarities of nature. 
Dr. Burks, who prepared the following 
treatise, obtained the B.A. degree in 1933, 
the M.A. in 1934, and the Ph.D. in 1937, 
all from the University of Illinois. On July 
1, 1937, he joined the staff of the Natural 
History Survey. But for short leaves during 
which he assisted at the United States National 
Museum, and leave for military service, he 
remained in the employ of this Survey until 
May 21, 1949. At that time, he resigned to 
take a position in the Division of Insect Iden- 
tification with the United States Department 
of Agriculture in Washington, D. C. 
A number of people have been of assistance 
in the preparation of this manuscript. We 
are especially indebted to Dr. Carl O. Mohr 
for his excellent illustrations, to Mrs. Eliza- 
beth Maxwell for the preparation of many of 
the line drawings, and to Mrs. Leonora K. 
Gloyd for her careful and painstaking work in 
the later stages of preparation of the manu- 
script for publication. 
For permission to use figs. 88, 188-192, 218, 
and 300, most of them redrawn without ap- 
preciable change from Traver in The Biology 
of Mayflies, we are indebted to the Comstock 
Publishing Company. For loan of critical 
material for study, we are grateful to Dr. 
Henry Dietrich of Cornell University, Dr. 
Joseph C. Bequaert of the Museum of Com- 
parative Zoology, Harvard University, Dr. 
C. E. Mickel of the University of Minnesota, 
and Mr. W. J. Brown and Mr. G. P. Holland 
of the Canadian National Museum. 
Hartow B. Mitts, Chief 
Illinois Natural History Survey 
Urbana, Illinois 
