Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



in other localities. The stream originates in 

 the swamps and lakes of northern and 

 western Indiana, flows through the lower 

 portion of the northeastern eighth of Illi- 

 nois and empties into the Illinois River a 

 few miles west of Joliet. The water is 

 always colder than in our other rivers, al- 

 most always clear and in Illinois passes over 

 three swift rapids. The first rapids are at 

 Momence and are caused by a limestone out- 

 crop over which the river flovv^s; htXow the 

 outcrop the river gradually slows and in 

 this portion are luxurious beds of eel grass 

 which extend almost the full width of the 

 river bottom. The second rapids are at 

 Kankakee, extending from the foot of a 

 power dam about one-third of a mile down- 

 stream; here the river is wider and shal- 

 lower, and the bottom more gravelly, than 

 at Momence. The third rapids are at Wil- 

 mington, also below a power dam, but near- 

 ly a mile long; here the bottom has the 

 swiftest portion strewn with boulders and 

 the steepest gradient of all three rapids. 



There is a remarkable difference in the 

 taxonomic composition of the caddis flies 

 found in each rapids. Certain species unique 

 to the river are common to all three rapids, 

 but others may be very abundant at one 

 and rare or entirely lacking in the other 

 two. For instance, Brachycentrus numer- 

 osiis and lateralis and Alicrasema rusticum 

 are all very abundant at Momence but have 

 never been taken at Kankakee or Wilming- 

 ton. Hydropsyche cuanis occurs in countless 

 swarms at Wilmington but is a rarity at 

 the other two rapids. Hydropsyche aerata 

 is very common at Kankakee but is rare 

 at the other two. Hydroptila albicornis is 

 common to all three rapids but is found 

 nowhere else in Illinois. There is no doubt 

 that the physiological attributes of the water 

 are quite different at the three points de- 

 scribed, and these differences are likely due 

 to the effect of the power dams and the 

 sewage affluent which goes into the river 

 below each city. 



Rock River. — This river, running diag- 

 onally across the northwestern eighth of the 

 state, is essentially a clear, swift, cold-water 

 stream with a rock or gravel bottom. In 

 the early 1900's it was an unusually rich 

 stream from the standpoint of large variety 

 and num.bers of fish, but affluent from fac- 

 tories, city sewage and silt-laden drainage 

 ditches have altered the stream considerably. 

 The caddis flies found there today, how- 



ever, show distinctive features in contrast 

 to those of other streams. This is the only 

 river in which Hydropsyche bifida occurs in 

 large numbers; it is one of the few streams 

 in which we have taken Athripsodes men- 

 tieus, Chimarra obscura and Hydropsyche 

 valanis; and it is the only stream where we 

 have taken the northern Limnephilus moes- 

 tus. 



Tributary Streams 



Collecting in the smaller rivers and creeks 

 soon shows that as the size of the stream 

 decreases the potentialities for a varied 

 fauna increase. The species mentioned as 

 abundant in the large rivers are found also 

 in these smaller streams but in smaller num- 

 bers; conversely, we find here in numbers 

 species which are usually rare in river col- 

 lections. These include, among the net- and 

 web-spinning groups, Cheumatopsyche ana- 

 lis, oxa and aphanta, Hydropsyche bronta 

 and arinale, Nyctiophylax vestitus and Poly- 

 centropus cinereus. The case makers are 

 represented by a great variety of the 

 "micros," or Hydroptilidae, such Limne- 

 philidae as Pycnopsyche and Caborius, and 

 a great variety of Leptoceridae, especially 

 species of Athripsodes, Triaenodes and 

 Oecetis. 



Most of these small streams, as stated 

 above, are similar in general characteristics 

 to the large rivers. They are sluggish, silt 

 laden for much of the year and have fairly 

 warm water. Most of the species have 

 continuous generations from late spring to 

 early autumn and few of them are early 

 seasonal forms. The chief exceptions to this 

 are the Limnephilidae mentioned above, 

 which aestivate during the summer and 

 transform only in autumn, and our only 

 common species of Rhyacophilidae, Rhya- 

 cophila lobifera, which has only one genera- 

 tion, maturing early in spring. 



Ozark Hills Streams 



In the southern tip of Illinois there is a 

 small range of hills reaching an elevation 

 of about a thousand feet. These are one of 

 the eastern remnants of the Ozark Moun- 

 tains. In these hills are numerous streams 

 quite different from the usual type found 

 in the northern part of the state. They have 

 rocky beds, and in winter "and spring they 

 are swift and clear. Green moss grows in 



