16 



Illinois Natural History Survey Bulletin 



Vol. 23, Art. 1 



fully handled to avoid rubbing in transit and 

 in pinning. 



Adult Collecting 



Adults of most caddis flies come to lights 

 readily on warm nights having neither wind 

 nor a bright moon. Collecting at lights is 

 thus a profitable source of material. In 

 towns, illuminated store windows and signs 

 attract many of these insects and provide 

 convenient collecting points. 



Vapor Glow-Tubes. — Adult Trichoptera 

 are attracted very strongly to blue light 

 and hence are to be found most abundantly 

 around blue "neon" lights, or glow-tubes. 

 Fortunately for the entomologist many of 

 these blue lights can be found in towns and 

 these will serve as good concentration points 

 for caddis flies. At points where such lights 

 are not available we have had very good 

 success with a portable mercury glow-tube 

 which emits a strong blue light and is very 

 attractive to Trichoptera and many other 

 insects. This is described in detail by Burks, 

 Ross & Prison (1938). 



Automobile Headlights. — Another type 

 of night collecting we have found efiEective 

 at points away from towns is as follows. 

 Drive an automobile to a spot overlooking 

 a stream or lake and turn on the bright 

 lights. Into a shallow pan, such as a pie 

 pan, pour enough alcohol to cover the bot- 

 tom with from one-eighth to one-fourth inch 

 of liquid. Hold the pan directly under a 

 headlight. If aquatic insects are on the 

 wing, they will come to the light and eventu- 

 ally drop into the liquid, which traps them. 

 With a small piece of wet cardboard, scrape 

 the entire insect contents of the pan into 

 a small bottle of alcohol, which should then 

 be labeled, location, name of collector and 

 place being given. 



If few insects fly to the car lights, it is 

 convenient to dispense with the pan. In this 

 case the caddis flies may be picked off the 

 light easily by dipping an index finger in 

 alcohol, "scooping up" the insect rapidly but 

 gently on the wet surface and then dipping 

 it in the bottle. An aspirator, or sucker, 

 also can be used with success. 



Sweeping. — For daylight collecting, 

 sweeping often proves effective. Resting 

 places differ widely with the species, but 

 most caddis flies prefer shaded, humid places. 

 For these, sweep vegetation overhanging the 

 water, whether it is herbage nearly trailing 



in the water or boughs which hang above it. 

 I have noticed that many times the flies 

 seem to prefer (for resting places) conifer- 

 ous trees near the stream, and heavy beat- 

 ing of these is usually profitable. Some- 

 times the flies are numerous in bark crevices 

 of large tree trunks along stream banks; 

 here they are extremely difficult to detect, 

 for they mimic bark to a remarkable degree 

 when their wings are folded. Be sure to 

 have your net ready when you examine a 

 tree trunk, because the flies dodge and fly 

 with surprising speed when alarmed. 



Bridges. — One of the favorite resting 

 places of adult Trichoptera is the shaded, 

 damp, underside of a concrete bridge. When 

 other collecting fails it is sometimes possible 

 to pick up from a few to many caddis flies 

 resting under a highway bridge. Here again 

 the flies are wary, and must be approached 

 with caution and a ready net. 



Along the Water's Edge. — Frequently 

 the adults may be captured on stones, sticks 

 and vegetation in the water. This is true 

 especially of the Rhyacophilidae. A method 

 which sometimes gives good results is to 

 press floating vegetation, such as water 

 cress, until it is slightly submerged. Any 

 adults resting in this foliage will swim to 

 the surface in a moment or two. 



Collecting Larvae and Pupae 



All Nearctic caddis flies are aquatic in 

 the developmental stages. For this reason 

 almost any water habitat has possibilities 

 for the collection of larvae and pupae. 

 These should be preserved in liquid, prefer- 

 ably 80 per cent grain alcohol, as with the 

 adults. If vials are filled with larvae, the 

 liquid should be changed a few hours after 

 collection. 



The easiest way to start a search for 

 these immature stages is to turn over stones 

 and logs in riffles and rapids; if present, 

 larvae and cases may be found without 

 difficulty in these situations. Handfuls of 

 drift, weeds from the stream or river bot- 

 tom, and debris may be laid on the bank, 

 and the caddis fly larvae may be picked out 

 as they begin to move, at which time they 

 are easily detected. 



Cocoons of caddis flies may generally be 

 identified because they are securely fastened 

 to some object. These should be removed 

 very carefully, in order to avoid breaking 

 the silk membranes more than necessary. 



