Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



maturity of the eggs within the body of the 

 female, which then hiys the eggs in the 

 water, beginning the cycle again. 



Detailed accounts of various phases of 

 caddis fly life histories have been written 

 by many authors and constitute an extensive 

 literature. This was summarized by Betten 

 in 1934 and again, very extensively and com- 

 pletely, by Balduf in 1939. Consequently, 

 only a brief resume of the biology is given 

 here. In our Illinois studies, we have 

 stressed the taxonomic aspects; so the fol- 

 lowing information concerning oviposition is 

 drawn almost entirely from the two sources 

 mentioned above. 



Eggs and Oviposition 



Caddis flies lay many eggs, the number 

 probably ranging from 300 to 1,000 per 

 female. Considerable information is known 

 regarding the manner and place in which 

 these eggs are deposited, but a tremendous 

 amount remains to be observed. 



The adult females of Rhyacophilidae, 

 Philopotamidae, Psychomyiidae, Hydropsy- 

 chidae and Hydroptilidae enter the water 

 and there lay strings of eggs, fig. \B, on 

 stones or other objects. These strings are 

 usually grouped to form irregular masses, 

 each containing from a few to 800 eggs. The 

 eggs are surrounded by a thin, cement-like 

 matrix. 



Females of other caddis fly families usual- 

 ly extrude the eggs and form them into a 

 mass at the end of the abdomen before de- 

 positing them. These masses are usually 

 irregular or ovoid, but in some genera are 

 very definite in form, as, for example, the 

 genus Triaenodes, in which the eggs are 

 arranged in a flat oval, fig. \A. In all egg 



Fig. 1. — Eggs of caddis flies. A, Triae- 

 nodes tarda\ B, Cyrnellus marginalis. 



masses the matrix surrounding the egg is 

 gelatinous and swells upon absorbing mois- 

 ture. 



The Leptoceridae, Phryganeidae, Molan- 

 nidae and Brachycentridae usually attach 

 the egg masses to submerged stones, logs or 

 vegetation. The females of some of these 

 have been observed entering the water or 

 putting the abdomen into it for this purpose. 

 Other families, such as Helicopsychidae, 

 Goeridae, Lepidostomatidae and Sericosto- 

 matidae, deposit the egg masses in or near 

 the water, apparently as frequently one way 

 as the other. When not laid in the water, 

 the masses are usually placed near it. 



The family Limnephllidae has been the 

 subject of interesting observations and spec- 

 ulations. The egg masses are deposited 

 above the water on plants or stones which 

 protrude above it, on objects along the 

 shore or sometimes on twigs high in trees. 

 In this last case the gelatinous mass may 

 liquefy with rain, and the drops so formed 

 run down the twigs and drop into the water, 

 carrying young larvae with them. Evidence 

 of actual migration to water of young 

 larvae hatched from egg masses far from 

 the water's edge has not been demonstrated. 

 Rain probably plays an important part in 

 this phenomenon. 



Larval Habits 



Mode of Living. — Possibly the most in- 

 teresting, and certainly the most startling, 

 aspect of caddis fly biologies is the construc- 

 tion, by many species, of houses in which 

 they live. Not all species have these houses, 

 and many of the houses are of different 

 types. Much has been written regarding 

 possible classifications of these habits, in- 

 cluding the formulation of complex systems 

 and explanations. I believe, however, that 

 the following brief synopsis will present 

 most of the pertinent data. 



Free-Living Forms. — The larvae of the 

 genus Rhyacophila are completely free liv- 

 ing, having no case or shelter; they lay a 

 thread trail and have many modifications 

 for free life in flowing water, including 

 widely spaced, strong legs and large, strong 

 anal hooks, fig. 133. For pupation they form 

 a stone case or cocoon. 



Also free living are the early instars of 

 many Hydroptilidae (see p. 160). 



Net-Spinning Forms. — Larvae of Hydro- 

 psychidae, Philopotamidae and Psychomy- 



