Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



Purse-Case Makers. — Following exactly 

 the same principle as the above are many 

 cases of the Hydroptilidae. In general ap- 

 pearance they resemble a purse, fig. 465. 

 The larva occupies the case with the head 

 and legs projecting out of a slit in the front 

 margin while the anal hooks project out of 

 a slit in the posterior margin. For pupa- 

 tion, however, the case is cemented along 

 one side to a support and the slits are 

 cemented shut to form the pupal chamber. 

 Not all Hydroptilidae have cases of this 

 type, some of them having true cases (see 

 p. 160). 



Case Makers. — All caddis fly larvae ex- 

 cept those listed above make portable cases 

 which the larvae drag with them in their 

 daily movements. These cases are usually 

 made of pieces of leaves, bits of twigs, sand 

 grains or stones which are cemented or tied 

 together with silk. Rarely the case is made 

 entirely of silk. Case construction varies a 

 great deal from one group to another, from 

 one species to another within the same 

 genus, and frequently within the same spe- 

 cies. In general, cases subject to greatest 

 stream current are the most solidly con- 

 structed, whereas those in small ponds 

 where there is scarcely any water movement 

 are the most loosely constructed. 



For pupation the case is anchored to a 

 support and a top added to the case; the 

 pupa is formed inside this shelter and no 

 additional cocoon is made. 



Feeding Habits. — Most caddis fly larvae 

 are practically omnivorous, eating whatever 

 comes to hand. Such forms as the Hydro- 

 psychidae and Limnephilidae eat a prepon- 

 derance of plankton, sessile diatom growths 

 and other small organisms, but if opportun- 

 ity affords they will eat insect larvae and 

 often each other. When their populations 

 become crowded, caddis fly larvae are can- 

 nibalistic to a high degree. 



Certain genera are primarily predaceous, 

 the most notable ones being Rhyacophila and 

 Oecetis. Examination of stomach contents 

 shows that both of these are voracious 

 eaters; we have found 40 to 60 Chironomi- 

 dae larvae in single individuals of Rhya- 

 cophila, the alimentary tract being crowded 

 with these midge larvae from one end to 

 the other. In these two genera the mandi- 

 bles are long and narrow, apparently fitted 

 for grasping prey of this type. Such man- 

 dibles do not occur in phytophagous forms 

 which may be cannibalistic. 



The order Trichoptera as a whole, how- 

 ever, may be characterized as one in which 

 the minute aquatic life is assimilated and 

 converted to units of larger size which are 

 in turn usable by a variety of larger organ- 

 isms. 



Respiration. — This function in the Tri- 

 choptera is accomplished by cutaneous ex- 

 change or by gills. It varies greatly within 

 families and genera. Usually the larvae 

 of greater size have the larger or more 

 abundant gills, and the small larvae have 

 no gills at all. This is by no means a gen- 

 eral rule throughout the order. In those 

 species having gills, gill pattern and type 

 is almost uniform throughout the entire 

 period of larval growth, from the youngest 

 to the full-grown stage. 



Adult Habits 



Caddis flies include many strong fliers, 

 such as Macronemum, but they also include 

 other genera that fly only short distances. 

 A few species have brachypterous or apter- 

 ous females which cannot fly but which run 

 with great agility. 



In daytime most of the caddis flies rest in 

 concealed crevices or on foliage in moist, 

 shaded glens bordering streams.. At dusk 

 the adults fly quite freely, often skimming 

 back and forth across a body of water just 

 above the surface. These flights are prob- 

 ably mating flights, since males are fre- 

 quently involved; observations indicate that 

 these flights are not correlated directly with 

 oviposition. 



The adults have mouthparts that are 

 adapted for the ingestion of liquid foods and 

 have no hard grinding parts for mastication 

 of hard foods. In some families such as the 

 Phryganeidae the end of the labium forms 

 a large, terminal membranous lobe similar 

 in general appearance to the proboscis of 

 higher Diptera. Records indicate that in 

 spite of having no other means of getting 

 food, adults of many species normally live 

 1 or 2 months,. and probably in all species 

 nearly a month. 



Oviposition is discussed in connection with 

 the eggs. 



Parasitism 



The only record of parasites of caddis 

 flies in North America was reported by 

 Mickel & Milliron (1939). They reared 



