THE ECONOMIC STATUS OP INSECTS AS A CLASS. 567 



In the Homoptera we have 9 families, all of which are injurious, except 

 that here and there a species has had a commercial value, like the lac 

 and dye insects. 



In the Heteroptera there are 11 families which are strictly plant 

 feeders ; 8 are strictly predaceous; 3 are both injurious and preda- 

 ceous, while the economic value of 13 is more or less doubtful. Most 

 of these last are aquatic and bave some value as fish food. 



The insects of the single family of the order Physaptera are injurious. 



In the Orthoptera we bave 1 family of strictly predaceous habits, 1 

 which has a mixed food and is partly injurious and partly beneficial, as 

 its species become scavengers ; the habits of 1 family are unknown, while 

 in the 4 remaining families the species are all injurious as destroyers of 

 vegetation. 



The insects of the single family of the order Euplexoptera are prob- 

 ably beneficial as predatory forms and scavengers. 



The single family of the order Mallophaga is injurious, containing 

 parasites of bi^ds and mammals. 



In the Corrodentia the habits of the insects of the single family are, 

 on the whole, of little economic importance, though the species are to 

 be classified in the main as scavengers. 



In the Isoptera the forms belonging to the two families are injurious. 



In the order Plecoptera the species of the single family are practi- 

 cally neutral in their economic relations, although they possess some 

 value as fish food. 



All of the insects of the single family of the order Odonata may be 

 called beneficial. The adults are predaceous upon other insects, and 

 are thus strictly beneficial, but the larvae may in a sense be termed 

 injurious, since they are aquatic and prey upon other aquatic insects 

 which themselves may be food for fishes. 



The insects of the single family of the order Bphemerida are of little 

 economic value, except that they are important fish food. 



Lastly, the insects of eight of the families of Thysanura are beneficial 

 as scavengers and soil makers, while some of the species of one family 

 are somewhat harmful from the damage which they do in households. 



Tabulating the facts thus gained we have the following : Injurious as 

 feeding upon cultivated and useful plants, the insects of 112 families; 

 injurious as parasitic upon warm-blooded animals, the insects of 1 

 family; beneficial as preying upon other insects, the insects of 79 fami- 

 lies; beneficial as scavengers, the insects of 32 families; beneficial as 

 pollenizers only, the insects of 2 families; beneficial as forming food for 

 food-fishes, the insects of 3 families; of undetermined economic impor- 

 tance, the insects of 49 families; families containing both injurious and 

 beneficial forms, 22 families. The totals are: Beneficial, the insects 

 of J 13 families; injurious,, the insects of 116 families j both, or unde- 

 termined? the insects of 71 families. 



