THEIR RELATION TO EACH OTHER 95 



These bugs are of considerable importance as checks 

 to certain plant feeders and as they feed in the same 

 way throughout their life, each individual accounts 

 for a notable number of victims. Their weak point 

 is the limited power of reproduction. Most of them 

 lay only a small number of eggs and have only a single 

 or at most two broods during the season. As a control 

 factor, therefore, they lack flexibility and do not rise 

 to any sudden increase in the plant feeders. There is 

 a common species that in New Jersey feeds on the 

 larvae of the elm-leaf beetle, and each season is busily 

 engaged on the infested trees in fair numbers. In 

 years when the beetle is not abundant the marks of 

 its feeding are quite conspicuous; but in a season when 

 the beetle is unusually plentiful and destructive, the 

 bugs are present in almost exactly the same numbers 

 and their work is absolutely unnoticeable when effec- 

 tiveness is most urgently needed, nor does there seem 

 to be any considerable increase during the season fol- 

 lowing such an abundance. This same feature exists 

 with most of the species known to me and limits their 

 usefulness to very narrow bounds; they constitute 

 one check which is almost a fixed quantity and to which 

 the host insects are adapted. 



The order Orthoptera, including roaches, grass- 

 hoppers, locusts, crickets and the like, contains no true 

 parasites and but few predatory forms. Some of the 

 roaches are omnivorous and pick up occasional speci- 

 mens of insects and animal matter; but they can 

 scarcely be ranked as important checks to any other 

 species. And so the Mantids or soothsayers are vora- 

 cious feeders, preying upon almost any sort of insects 

 which they can secure; but they are few in number 

 both as to species and specimens, while their food is 

 so various that they are not of importance in the life 



