INSECT ENEMIES OF THE LOCUST. 285 



bring about a natural balance. It is because of the great fecundity of 

 insects, whether phytophagous or carnivorous, that there often occur 

 such comparatively sudden changes from excess to scarcity. A particu- 

 lar plant-feeder will swarm to an alarming and injurious extent one year^ 

 and be scarcely heard of the next. The locust shares with other species 

 in this particular. A period of excess is sure to be followed by a period 

 of scarcity, due largely to the increase of its natural enemies. This was 

 very fully illustrated last year; for on all sides the abundance of these 

 natural enemies was observed. Not to speak now of birds and other 

 larger enemies, it was matter of common remark in Minnesota that in 

 many localities where the locust eggs were laid in unusually great num- 

 bers, the hatching the following spring was nothing like so extensive as 

 was anticipated, on account of the destruction occasioned by grubs, 

 mites, &c. From every State and Territory where eggs were thickly 

 deposited, similar experience has been obtained. The locusts, after 

 hatching, were attacked to an unusual extent by the various enemies 

 to be presently enumerated, while careful observers in British America 

 had already noticed, in 1876, that the locusts which occurred there were 

 so loaded with parasites that they died without laying eggs ', and the 

 Immunity from locust injury enjoyed there in 1877 is attributed largely 

 to this cause. 



It has been our privilege to watch quite closely the working of these 

 more minute locust enemies during the past few years, and their useful- 

 ness is altogether underrated, for the simple reason that their work too 

 often goes on hidden and unobserved. Considering the great abundance 

 in which they sometimes occur, and their great assistance in keeping 

 our Eocky Mountain locust in check, it is surprising how little is said of 

 or attributed to insect enemies of the European migratory locusts by 

 European writers. Gerstacker, speaking oi migratoria^ says that it has 

 no insect enemy worthy of mention, and cites only field crickets, a large 

 locust {Locusta viridissima, L.), a Mantis, and the hair-worms. Koppen 

 adds ants and a ground-beetle {Calosoma) ', but it is plain that neither 

 of these late writers have had much personal experience in the matter. 



The invertebrate enemies of our locust may, to facilitate reference, be 

 divided into, 1st, those which affect the eggsj 2d, those which affect 

 the active locust. 



ANIMALS THAT DESTROY THE EGGS. 



The Anthomyia Egg-parasite {AntJwmyia angustifrons, Meigeh, 

 Fig. 21). — This is, perhaps, the most common and wide-spread of all the 

 different egg-enemies, and in the fall of 1876 it destroyetl on an average 

 about ten per cent, of the eggs in Missouri, Kansas, and Nebraska, and 

 in some localities a much larger percentage. It was dso quite common 

 in Iowa and Minnesota, and, as we learned during the i)ast year, occurs 

 in Colorado and Texas. It is doubtless this species which our corre- 

 spondents in many cases refer to by the general term of "grubs," "white 



