19 



Being predaceous, they exert a considerable influence upon the insect 



life of the sand prairie. 



Brytheuiis simplicicoUis Say. July, August. 



This dragon-lly is the most abundant species of early summer in 

 the river district. It is very commonly seen at the Devil's Hole, and 

 is an important predaceous species of the bunch-grass. 



Sympctrum ruhicundulum Say. July 3. 



This dragon-fly is infrequent in sand prairie. One specimen was 

 taken in the bunch-grass pasture at the Devil's Hole. 



Peritheniis domitia Drury. June 28. 



Rather a common species, taken in bunch-grass at the Devil's Hole. 



Order orthoptera 



Isclnioptera sp. (indeterminable). April 4. 



In decaying log at the edge of the bunch-grass association. Prob- 

 ably inaequalis Sauss.-Zehnt. All v^^ere nymphs. This is a forest 

 species ; none of the Blattidae are typical sand-prairie forms. 



Family Acridiidae 



The Acridiidae, or locusts, are the dominant group of the Orthop- 

 tera. They usually hatch in spring and mature in summer, reaching 

 their maximum development late in smnmer. The food is almost 

 entirely vegetable, principally grasses. Some of the locusts are mi- 

 gratory. Those living in open plains usually have better powers 

 of flight than the locusts of thickets or forests. The Acridiidae are, 

 diurnal, non-social, and short-lived. They do not build nests or dig 

 holes ; they have not a high order of insect intelligence. They are 

 active only in the most favorable season. We may say that their 

 habits are very simple ; they have taken the simplest means to solve 

 the problem of existence. The locusts are best developed in warm 

 climates. In North America they are commonest in the southern and 

 southwestern parts, and in the prairie region. They are very sensitive 

 to local environmental differences, so that the species are good indices 

 in local distribution studies.* Terricolous species (those which are 

 found usually on the ground, not on the plants) are more suited to 

 dry treeless areas, in which the bare soil is considerably exposed. The 

 Acridiidae have very many enemies — mites, predaceous beetles, flies 

 and wasps, birds, reptiles, and mammals. They are one of the im- 

 portant sources of animal food supply. 



*The agreement in local distribution of grasshoppers and plant-communities 

 is the subject of a recent paper I)y the writer (Vestal, '13). 



