48 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 39 



larvae are wormlike and they live in streams, ponds, and lakes. 

 Many of them build cases of sticks, stones, or sand and move 

 about with only the front end of the body protruding from the 

 case. When disturbed, the larvae withdraw completely into the 

 cases and are then very difficult to see. The adult fly and larva 

 of Rhyacophila fenestra Ross illustrate this order, figs. 50 and 

 51. In many aquatic situations, caddisflies are the predominant 

 small animal life and are an important factor in fish food econ- 

 omy. Also, they are stream pollution indicators. 



Lepidoptera Insects with two pairs of wings, long anten- 



Butterflies, nae, and with mouthparts forming a long 



Moths sucking tube. The body and wings are cov- 



ered with a dense mass of scales, charac- 

 teristic of this order, fig. 52. The young are known as cater- 

 pillars or grubs. The larval stage in this order is well exemplified 

 by one of the cabbage webworms, Hellula undalis Fabricius, fig. 

 53. Some other larvae are hairy ; still others are sluglike. 

 To this order belong not only a very large number of species, 

 but also a very large number that are especially injurious to 



Fig. 52. — Lepidop- 

 tera. A typical moth 

 showing scales on 

 wings and body, and 

 the sucking tube, 

 which is coiled up 

 under the head when 

 not in use. Species 

 of this order occur- 

 ring in Illinois in- 

 clude specimens that 

 vary in size from 0.1 

 inch to several inch- 

 es. The largest of 

 these insects have a 

 wingspread of over 

 5 inches. 



agriculture. These include such species as the codling moth, 

 cabbage moth, butterflies, the entire cutworm group, and a host 

 of others. In addition, the various clothes moths, which are a 

 constant source of loss to householders, and various species of 

 meal moths, which cause tremendous damage to stored grain 

 every year, are members of this order. 



