1 76 ARTHUR G. VESTAL. 



3. Species which mature in spring or early summer, but which remain abundant 



until frost. Chlcealtis conspersa, Melanoplus angustipenni's, M. atlanis, M. 

 femur-rubrum. The last two are known to be two-brooded, and M. angusti- 

 pennis probably is also, in parts of its range. 



4. Species which mature in early July, remaining active until frosts. This is 



the common grasshopper life-history. Stcnobothrus curtipennis, Camnula 

 pellucida, Dissosteira Carolina, Spharagemon bolli, Scirtetica marmorata, 

 Circotettix verruculatus, Melanoplus islandicus, M, luridus. 



5. Late-maturing species, appearing from late in July to the middle of August, 



and remaining until frosts. Arphia pseudonietana, Podisma glacialis variegata, 

 M. differentialis. 



The different timing of the period of activity of the species may 

 be correlated with one or both of two kinds of seasonal difference 

 in environmental influence: (i) Changes in physical and vegeta- 

 tional conditions necessary for the various activities. Conditions 

 of temperature, moisture, vegetation, etc., change so materially 

 with the season as to present very different environments for 

 animals at different times of the year. Grasshoppers of different 

 habitat-preferences may perhaps occupy the same area at 

 different seasons. Life-histories are affected by geographic 

 variation of climatic conditions. The entire complex of behavior 

 characters of the animal is intimately associated with its life- 

 history (Shelford, '12^: 334). (2) Seasonal differences in an- 

 tagonistic influence of other animals, particularly those of similar 

 requirements. These influences among animals which eat the 

 roots of the corn plant and the strawberry plant are discussed 

 by Forbes ('09: 296). Different species of certain insect genera, 

 .among them Arphia and Hippiscus, which are of similar habits 

 and which occur in the same association, sometimes are active 

 during successive parts of the season. One species of a genus 

 may be completely replaced by another in a very short time, the 

 second species continuing abundantly during the remainder of 

 the season (Vestal, 'i3&). This replacement of one insect by 

 another of similar habits is not uncommon among species of 

 one genus, though not confined within genera. The differences 

 in time of appearance among all the grasshopper species within 

 a region, with the result that within some of the associations 

 fewer species occur together at one time, may perhaps be ac- 

 counted for partly in terms of antagonistic animal influence. 

 The fact that grasshopper species of unique habits, which occupy 



