Xo. Iil53] 



FOOD-PLAMS AXD IXSECTS 



321 



tunneling larvae remain in a moist burrow where evapora- 

 tion is very slow. Similarly the animal materials utilized 

 as food are very low in water content. That we do not 

 find Lepidopterous larvae in moist material of animal 

 origin is no doubt due to the fact that they do not appear 

 to be adapted for subsistence upon the abundant micro- 

 organisms present in such materials. 



Passing to a consideration of the phytophagous Lepi- 

 doptera, by far the greater part of the order remains to 

 be dealt with. As indicated in the tabulation, practically 

 all of these occur on the higher plants and feed almost 

 always upon living tissue. The latter is true almost with- 

 out exception of the leaf-feeding forms, although one of 

 our common moths of the eastern states, Pyromorplia, is 

 known to live upon dead and decaying fallen leaves and 

 another of our small moths avails itself of hemlock chips. 

 Among those which live in woody tissue, some prefer 

 weakened or sickly trees or unhealthy branches, but al- 

 most none occur in dead wood. 



Of those living on the lower plants, one small family 

 of moths, the Lithosiidae, subsist upon lichens and they 

 are almost the only ones affecting these plants. This 

 family is far from primitive, so that its association with 

 a series of lower plants could have no significance, even 

 if it were definitely known that the lichens are a very old 

 group, which does not seem probable. 



Mycetophagous forms of Lepidopterous caterpillars 

 are of very unusual occurrence, in spite of the fact that 

 several large series of beetle larvae develop in fungi. 

 They are found, however, and there are in North America 

 at least two species of Tinea which have been bred from 

 these plants. 



In spite of the similarity, of their foliage to that of the 

 flowering plants, ferns do not commonly serve as food 

 plants for insects. They are, in fact, strikingly immune 

 from insect pests of all sorts. This is hardly what might 

 be expected from the long presence of this group of 

 plants, their enormous development in the past, and their 



