August, 1944 



Ross: Caddis Flies of Illinois 



iidae spin a fixed abode which is fastened 

 to plants or other supports in the water, 

 sometimes in still water but more frequent- 

 ly 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, fig. 2. These are long, 

 narrow pockets of fine mesh, with the front 

 end anchored upstream, the remainder trail- 

 ing behind with the current. They are built 

 by the Philopotamidae. 



2. — Trumpet nets, fig. 3. 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, fig. 4. Peculiar to 

 the family Hydropsychidae is the habit of 

 erecting a net directly in front of a tubelike 



Fig. 2. — Finger 

 nets ot C hi 711*117-7 a 

 aterri7na. (After 

 Noyes.) 



retreat concealed in a crevice or camouflaged 

 by bits of wood, leaves or similar material. 

 These nets may be erected between two sup- 

 ports in the open, as in the case of Potamyta, 

 or the net may be constructed as one side 

 of an antechamber, as in the case of many 

 species of Hydropsyche, fig. 4. 



In all these types the caddis fly larva 

 cleans the food and debris off the net, ingest- 

 ing anything edible swept into it by the 

 current. Normally the larva spends most 

 of its time with its head near the net ready 

 to pounce on any prey. When disturbed, 

 it backs out of the net or retreats with 

 great agility. The flexible body structure 

 enables the larva to move backward rapid- 

 ly, but it can move forward only slowly. 



T ube-Maki/ig Forms. — Some psychomyiid 

 larvae, notably of the genus Phylocentropus, 

 burrow into sand at the bottom of streams, 

 cementing the walls of the burrow into a 

 fairly rigid structure which may be dug out 

 intact. The mechanics of food gathering in 

 this group are not well understood. 



Fig. 3. — Trumpet net ot Polycent7opiis sp. 

 (After Noyes.) 





mCi':mm''i 



Fig. 4. — -Nets of Hydropsyche. A, dia- 

 grammatic figure of house; at the left is the 

 tube in which the larva lives; in front of it is a 

 vestibule having a catching surface with a fine 

 mesh in the side wall; near this net is the open- 

 ing of the larval tube. (After Wesenberg- 

 Lund.) 5, net spun over a crevice of a sub- 

 merged stick which houses the larva. (After 

 Comstock.) 



In both the net-spinning and tube-making 

 forms, pupation takes place in the end of the 

 tube or retreat. The larva constructs a 

 cocoon of leaf fragments, stones or what- 

 ever other material is available, lining it 

 with silk. The pupa is formed here. 



Saddle-Case Makers. — Larvae of the rhy- 

 acophilid subfamily Glossosomatinae make 

 a portable case which consists of an oval 

 top made of stones and a ventral strap made 

 of the same material, fig. 136. The larva 

 proceeds with its head and legs projecting 

 down in front of the strap and the anal 

 hooks projecting down at the back of the 

 strap. For pupation, the strap is cut away 

 and the oval dome is cemented to a support, 

 the pupa being formed in the stone cell thus 

 made. 



