566 THE ECONOMIC STATUS OF INSECTS AS A CLASS. 



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 2 are strictly plant-feeding; the 

 Cynipidse, or gall flies, are in the main injurious to plants, but some 

 forms are parasitic; 9 families are strictly parasitic upon other insects; 

 15 are predatory upon other insects; 2, comprising the bees, have no 

 other especial value in their relations with man than as pollenizers of 

 plants or producers of honey; 3, comprising the ants, are beneficial as 

 scavengers, but injurious in their other relations. It must be remem- 

 bered, however, that at least 27 of the 33 families are of the greatest 

 value in the cross fertilization 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 

 9 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 practically no 

 economic importance, although certain of them visit flowers; 2 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 par- 

 asitic 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, approximately, 

 injurious families, 10 ; predaceous families, 11 ; parasitic family, 1 ; scav- 

 engers, 19. In point of numbers of individuals in this order, as well 

 as in the Coleoptera, no doubt the injurious will exceed the predaceous, 

 while in the Diptera the scavengers will probably equal all of the oth- 

 ers put together. 



In the Lepidoptera practically all of the sixty-odd families are inju- 

 rious through the damage done by their larva; 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 fertilization. 



In the Trichoptera the insects of the single family feed upon aquatic 

 plants and have no economic value except as furnishing food for food- 

 fishes. 



The insects of the single family in the order Mecoptera are indiffer- 

 ent in their economic relations, though probably slightly beneficial. 



In the ISTeuroptera all of the 7 families are beneficial through their 

 predaceous habits, with the exception of the Sialidse, which, since their 

 larvae are aquatic, may be termed indifferent or neutral, though it has 

 both a beneficial and injurious relation to food-fishes. 



