SPIDERS. 173 



Insects. 



A detailed account of the chief useful insects follows in 

 Chapter V. Their number, especially that of ground-beetles, 

 ichneumon-wasps and Tachinae, increases steadily with that 

 of the destructive insects ; this fact is all the more important 

 as the activity of mammals and birds altogether fails to 

 combat such calamities successfully. 



Spiders. 



Spiders (Arachnoidea) include two distinct families of insect- 

 destroyers, Araneinae and Phalangiinae, both of which are 

 great destroyers of insects. The common garden-spider 

 (Epeira diadema, Cl.) and Steatoda sisypliia, Cl., may be taken 

 as examples of the former class, and the common harvest-man 

 (Plialangiwn parietinum, de Geer) of the other. The first 

 catches many small beetles and other insects in its large 

 vertical nets expanded in the underwood of forests, the second 

 species destroys large numbers of "Lopliyrus pini, L., as well 

 as other insects. The harvest-men become very active in the 

 evening, moving about rapidly with their long stilt-like legs, 

 and preying on small insects, plant-lice, etc. 



The web-making spiders may do some slight injury to 

 plants by their webs, which interfere with the full development 

 of blossoms and foliage. 



Myriapoda. 



Centipedes, of which Lithobiusforjicatus, L., is an example, 

 and millipedes, for instance, lulus terrestris, L., live under 

 bark, stones, and moss, and kill numbers of insects, also slugs 

 and snails. Species of lulus also attack fleshy roots in gardens 

 and fields, as well as wheat, and fruit such as strawberries ; 

 they also appear to cut off seedlings at the collar in a manner 

 similar to wireworms. 



3. Remedial Measures. 



In considering the measures to be taken in attacking insects, 

 we must select the proper season, and adopt means which do 



