THYSANOPTERA AND ORTHOPTERA. 193 



abundant in one place, whether or not it actually lacked room there, 

 would tend to spread to places where competition was less. If, con- 

 versely, a given species is found crowded in certain localities when other 

 similar, but less crowded, situations are open to it. it may safely be 

 taken for granted that the species does not disseminate readily. 

 The tendency to spread should A'ary inversely as the difference in the 

 numbers occupying the two neighboring similar situations, other things 

 being equal. 



This test was applied to determine the rapidity of dissemination of 

 Thysanoptera. A short time spent in collecting thrips in settled country 

 was sufficient to make it evident that even with the same species, in- 

 dividuals were more abundant in certain localities than in others only 

 a short distance away where, to all appearances, the conditions of life 

 were precisely the same. Thrips living among the florets of white 

 clover were collected in patches where the clover was eciually abundant, 

 and equally large and fresh; yet one patch often yielded many more 

 specimens on a given number of heads than did the other. 



Where this difference was noted, one of the localities where collections 

 were made was nearly always near a road, the other in a wood or field 

 a greater or less distance from the road. To test whether this were 

 generally true, different kinds of flowers were examined along differ- 

 ent kinds of roads. The character of the road was noted in every case, 

 especially as to its direction and the amount of travel over it. Some 

 roads running north and south, others east and west were examined. 

 Only such flowers were examined as nelded thrips in large enough 

 numbers to make a fair test, and care was taken to select flowers of ap- 

 proximately the same size and age. Two localities were examined 

 only when the flowers were about as abundant and as evenly distribut- 

 ed in one as in the other. No counts were made except where the two 

 localities were connected by a series of flowers as close together as in 

 the localities examined, so that migration from one to the other could 

 easily have been effected. Six flowers were examined in each locality. 

 Only one flower was examined on a single plant, and plants were selected 

 at about eciual intervals from each other in the two localities. The 

 results are given in Table I. 

 25 



