142 PHYSICAL GEOGKAPHY. 



Invertebrate Enemies. It is a law of nature that the undue devel- 

 opment of any animal is checked sooner or later by a like increase 

 of its natural enemies. Were it not for that law, the slowest breed- 

 ing species would soon overrun, to the exclusion of all other ani- 

 mals, its own special habitat. 



Among locust egg destroyers, no insect equals in efficacy the An- 

 thomyia egg-parasite (Anthomyia angustifrous}. A few were noticed 

 in 1874, and by 1876 it destroyed about ten per cent of the eggs in 

 Nebraska, and Prof. Thomas reports an equal destruction in Kansas,, 

 Missouri, Iowa and Minnesota. He also remarks that " we never 

 dug for five minutes among the locust eggs, anywhere in our 

 travels during May, without finding this parasite, in various stages 

 of development." It is a small white magot, and is found in the 

 locust egg pod extracting the juices and leaving nothing but dry 

 dissolved shells. From this magot is developed a small gray two- 

 winged fly, about one-fourth of an inch long. The common flesh 

 fly, many species of Ground, Blister, Soldier and Dick beetles, also 

 prey on locust eggs. 



After the locusts emerge from the eggs, their greatest insect enemy 

 is the Locust Mite (Trombidium locustarium}. It also preys on the 

 eggs. The parent mite lays from three to four hundred eggs, and 

 therefore increases at a prodigious rate. The young mite manages 

 to fasten itself on the locust, especially during and after rains, and 

 mostly lodges under the base of the wings. Such numbers are often 

 found lodged on single locusts as necessarily to produce death. 

 During locust flights, I have frequently seen hundreds fall to the 

 ground, which, on examination, proved to be partially destroyed by 

 these mites. Ground beetles, Asilus flies, Flesh flies, Digger 

 Wasps and Tachina flies, especially the latter, also feed on locusts 

 and destroy great numbers. Hair worms, Spiders, Soldier-bugs 

 and Dragon flies also prey on the locust. 



Vertebrate Enemies. Among vertebrates, no animals equal the 

 birds as destroyers of insects, and especially of locusts. The num- 

 bers of locusts which birds consume is simply incalculable. Many 

 species in locust years live entirely on them, and most do so par- 

 tially. Often each bird of a species captures several hundred during 

 each day. In fact, after many years' study of this subject, and after 

 dissecting more or less of several hundred species, I have been 

 forced to the conviction that even the gramnivorous birds cannot 

 be excluded from the list of locust enemies. The reader will find 



