February 17, 1899.] 



SCIENCE. 



245 



if possible, some liglit as to the relative 

 proportion of insects which are injurious or 

 beneficial. 



It will be manifestly impossible to cata- 

 logue the species or the genera in this way, 

 and it will be obvious that a classification 

 from families will be lacking in exactness, 

 since some of the families are very large in 

 number of species and others exceedingly 

 small ; but, taking the groups as a whole, 

 no better and speedier means suggests itself 

 than to summarize the habits by families. 



Another difiiculty, however, which arises 

 in such a classification is the fact that some 

 orders are in a much more advanced stage 

 of classification than others, and the force 

 which is given to a family as a taxonomic 

 group varies with the views of the latest 

 monographer. Nevertheless, taking only 

 the older and generally accepted families 

 and analyzing habits, we find the situation 

 to be as follows : 



Of 33 families of Hymenoptera, but two 

 are strictly plant-feeding ; the Cynipidse, or 

 gall flies, are in the main injurious to 

 plants, but some forms are parasitic ; nine 

 families are strictly parasitic upon other 

 insects ; fifteen are predatory upon other 

 insects ; two, comprising the bees, have no 

 other especial value in their relations with 

 man than as pollenizers of plants, or pro- 

 ducers of honey ; three, comprising the ants, 

 are beneficial as scavengers, but injurious 

 in their other relations. It must be re- 

 membered, however, that at least 27 of the 

 33 families are of the greatest value in the 

 cross-fei'tilization of plants, in which work 

 the insects of this order perhaps take the 

 lead. 



In the Coleoptera, or beetles, considering 

 82 families, the insects of nine families on 

 the whole are injurious, and of 23 families 

 on the whole are beneficial as destroying 

 injurious insects ; 10 families are beneficial 

 as scavengers, and 30, or more, mostly small 

 groups of little importance, contain some 



scavengers and many neutral forms of prac- 

 tically no economic importance, although 

 certain of them visit flowers ; two families 

 contain both injurious and beneficial forms, 

 as well as many that are neutral. 



In the Siphonaptera, or fleas, the species 

 of the single family are parasitic upon 

 warm-blooded animals. 



In the Diptera, or true flies, if we classify 

 the families according to habits of the 

 majority of the species in each, we get ap- 

 proximately : injurious families, 10; preda- 

 ceous families, 11; parasitic family, 1 ; scav- 

 engers, 19. In point of numbers, of indi- 

 viduals in this order, as well as in the 

 Coleoptera, no doubt the injurious will ex- 

 ceed the predaceous ; while in the Diptera 

 the scavengers will probably equal all of 

 the others put together. 



In the Lepidoptera practically all of the 

 60 odd families are injurious through the 

 damage done by their larvse to vegetation, 

 but here again it must be remembered — and 

 the same comment holds for many of the 

 Diptera which we have just considered — that 

 the adult insects are among the most active 

 and frequent visitors of flowers and have a 

 great and beneficial effect on cross-fertiliza- 

 tion. 



In the Trichoptera the insects of the 

 single family feed upon aquatic plants and 

 have no economic value except as furnish- 

 ing food for food fishes. 



The insects of the single family in the 

 order Mecoptera are indifferent in their 

 economic relations, though probably slightly 

 beneficial. 



In the ISTeuroptera all of the seven fami- 

 lies are beneficial through their predaceous 

 habits, with the exception of the Sialidie, 

 which, since their larvse are aquatic, may 

 be termed indifferent or neutral, though it 

 has both a beneficial and an injurious rela- 

 tion to food fishes. 



In the Homoptera we have nine families, 

 all of which are injurious except that here 



