26 ILLINOIS BIOLOGICAL MONOGRAPHS [146 



These data show that infection is local to a high degree and consequently 

 that infection must take place at the point where the larvae occur; in other 

 words, that the larvae are not widely distributed by an intermediate 

 carrier. The data also show that the host itself does not ordinarily migrate 

 very much during the summer. The migration of the average host seems 

 to be limited to a radius of about half a mile, perhaps less. 



Just how the larva enters the host I have not been able to discover. In 

 the spring of 1914 when the infection was so heavy I had not yet discovered 

 the host and in the two succeeding years the infection was ordinarily so low 

 that an attempt to work out that particular phase of the problem by obser- 

 vation in nature would have been a waste of time. 



It will be sufficient here to give a brief account of the habits of the hosts, 

 leaving the discussion of the possible modes of infection to be taken up 

 later. Altho the species of Orchelimum and Xiphidium found to be the 

 hosts of Gordius robustus are the common meadow Locustidae, they are 

 much more abundant in the tall grass near the water's edge than elsewhere. 

 Orchelimum vulgare and Orchelimum nigripes are found most abundant 

 right at the water's edge while Xiphidium nemorale is more abundant on 

 the taller weeds or on the banks of the streams. 



The species are omnivorous but feed chiefly on grass and weeds. 

 Several times I have found Orchelimum vulgare feeding on other insects. 

 In captivity all of the species are cannibals, feeding on each other even 

 when in larger cages. The collected grasshoppers had to be brought home 

 in tightly stoppered bottles in which the oxygen supply soon became so 

 low that the insects became quiescent, and even then they often injured 

 each other severely before they could be brought to the laboratory and 

 examined. 



Tho the species are so abundant on the grass near the border I have 

 never seen them deliberately entering the water. But their behavior differs 

 so greatly during the different times of the day that it is possible for them 

 to enter the water regularly at some time during the night or early morning 

 but never do so during the time at which my collections were made. The 

 specimens are most active during the early part of the day, especially when 

 the sun shines. Since all specimens were collected by hand, simply by 

 approaching slowly and grasping them suddenly, it was almost impossible 

 to get specimens during the forenoon or early afternoon of a hot, sunny day. 

 Altho on such days the males are singing everywhere, they become aware 

 of the approach and drop to the ground long before they are in reach. 

 Contrary to the habits of the Acrididae, these Locustidae never leap from 

 place to place to escape an enemy, but drop down almost perpendicularly 

 to a lower level in the grass or even to the ground. They either remain 

 quiet where they drop or run along for some distance and then remain 

 quiet so that it is almost impossible to find them. When situated on the 



