38 



THE ORTHOPTERA OF MINNESOTA. 



they can be found upon the stalks of plants, several feet 

 above the ground, or upon fences and outhouses, if such are 

 accessible. 



Social insects are more liable to epidemics than solitary 

 species, for in social species a constant contact with the 

 diseased objects as well as w^th the other members of the 

 same colony greatly facilitates the spread of a disease. 

 This explains, in part, w^hy a disease will spread much more 

 rapidly, and work more efifectualW, when insects occtir 

 together in large numbers, than when few and scattered. 

 The same thing occurs when an epidemic of yellow fever or 

 cholera sweeps through our land. How much more quicklj' 

 and fatally it works in our cities than in thinly populated 

 regions! Some of these diseases seem to force their victim 

 to wander about, and thus spread them in all directions. 

 Thus locusts attacked by the Locust-fungus {Empusa grilli 

 Fres.), invariably climb some tall weed or grass, and cling 

 to it long after death. 



Figure 11 shows a locust [Mela- 

 noplus bivittatus Say), w^hich has 

 been attacked by the fungus and 

 killed after it had climbed to the 

 top of a plant. The figure shows 

 w^ell the frantic efforts of the 

 locust to cling to its support. 

 This peculiar effect of the disease 

 to force the sick and dying insect 

 to cling to tall plants enables its 

 spores to infect a much wider area, 

 as they can from this elevated po- 

 sition fall on the food of the locusts 

 as well as on the locusts themselves. 

 This fungus has also the power 

 of throwing its spores to a consid- FiG.ii.—Meianopius bivittatus 



erale distance. killed by a fungus, original. 



Besides the minute parasites mentioned thus far, and 



