CHAPTER 10 



Trichoptera 



By D. G. Denning 

 Walnut Creek, California 



At present seventeen families, one hundred thirty-five 

 genera, and nine hundred eighty recognizable species 

 of caddisflies are known to occur in North America 

 north of Mexico. In California the comparable figures 

 are fourteen families, fifty-eight genera, and one hun- 

 dred and sixty-eight species. Thus 43 per cent of the 

 North American genera are represented but only 17 per 

 cent of the species. The only North American families 

 not yet recorded from the state are Beraeidae, Goeri- 

 dae, and Molannidae. The family Goeridae is known 

 to occur in Oregon and probably will be collected in 

 northern California. 



Adult caddisflies (or caddiceflies) are generally 

 small to moderate size, somber colored, and secretive. 

 The adults (fig. 10:1) may be distinguished from other 

 insects as follows: head with long, threadlike anten- 

 nae; mandibles vestigial; maxillary and labial palpi 

 well developed; two pairs of. wings (reduced in a few 

 females) held rooflike over the body and covered with 

 hairlike setae (in some genera with a few scattered 

 scales), fore wings slightly coriacious, hind wings 

 shorter but usually broader; and venation simple. 



The classification of adult Trichoptera is based 

 largely on the male genitalia. In most cases, species 

 identification is possible only by reference to these 

 characters, so species keys are given only to males. 

 In a few large genera such as Rhyacophila, species 

 keys are not given because monographic treatment is 

 needed but in such cases it is nevertheless possible 

 to determine California species by referring to the 

 illustrations. Because of their importance, figures of 

 genitalia have been reproduced for every species, 

 including a few original drawings of species not 

 illustrated with the original description. 



The eggs of caddisflies are deposited in or near 

 the water, either as strings or in a mass. The females 

 of such families as Rhyacophilidae, Philopotamidae, 

 Psychomyiidae, Hydropsychidae, and Hydroptilidae 

 enter the water to attach their eggs to submerged 

 objects. Others (Limnephilidae) may deposit their egg 

 masses above the water on various objects. 



The larvae are little known, only about 15 per cent 

 of the known species having been associated with 



the adults. The terminology commonly used in the 

 description of the larvae and pupae is illustrated in 

 figure 10:6. One of the best accounts of the various 

 larval types is given by Ross (1944) and is quoted 

 here. 



"Free-Living Forms. —The larvae of the genus Rhya- 

 cophila are completely free living, having no case or 

 shelter; they lay a thread trail and have many modifi- 

 cations for free life in flowing water, including widely 

 spaced, strong legs and large, strong anal hooks. 

 For pupation they form a stone case or cocoon. 



"Also free living are the early instars of many 

 Hydroptilidae. 



"Net- Spinning Forms. — Larvae of Hydropsychidae, 

 Philopotamidae and Psychomyiidae spin a fixed 

 abode which is fastened to plants or other supports 

 in the water, sometimes in still water but more fre- 

 quently in running water. Three common types of these 

 structures are found, all of them spun from silk and 

 forming some sort of net; when taken out of water 

 they collapse into a shapeless string. There is always 

 an escape exit at the end of the tube. 



"1. — Finger nets. These are long, narrow pockets 

 of fine mesh, with the front end anchored upstream, 

 the remainder trailing behind with the current. They 

 are built by the Philopotamidae (fig. 10:2e). 



"2. — Trumpet nets. In this type the opening of the 

 net is funnel-shaped, and the end is fastened in such 

 a way that the water movement distends the net into 

 a trumpet-shaped structure. This type of net is used 

 extensively by the Psychomyiidae. 



"3. — Hydropsychid net. Peculiar to the family 

 Hydropsychidae is the habit of erecting a net directly 

 in front of a tubelike retreat concealed in a crevice 

 or camouflaged by bits of wood, leaves, or similar 

 material. These nets may be erected between two 

 supports in the open, as in the case of Potamyia, or 

 the net may be constructed as one side of an ante- 

 chamber, as in the case of many species of Hydrop- 

 syche. 



"In all these types the caddisfly larva cleans the 

 food and debris off the net, ingesting anything edible 

 swept into it by the current. Normally the larva spends 



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