August, '14] McGREGOR: RED SPIDER CONTROL 329 



a point 600 feet from the source. The final affected area, semi- 

 circular in shape, comprised thirteen acres, and within its confines the 

 occurrence was general. While such a case as this is unusual, four- 

 acre or five-acre spots with from 25 to 100 per cent damage, are fre- 

 quently to be seen. 



As to the control of this pest, through the operation of natural 

 agencies, there is considerable to be said. As was previously inti- 

 mated, climatic conditions influence the development of the red spider 

 to a marked extent. During times of little rainfall and high tempera- 

 ture reproduction goes on by leaps and bounds; on the other hand, 

 long, heavy rains work havoc to the red spider population. In spite 

 of the fact that the mites inhabit the underside of the leaves, many 

 are washed off by rains and others are destroyed by the upward bom- 

 bardment of sand particles which may always be seen coating the lower 

 leaves after storms. In fact, it appears true that a few heavy rains, 

 especially if they continue for some time, reduce, for the time being at 

 least, the degree of infestation to a great extent. As noted before 

 under hydro-locomotion, however, we have demonstrated during the 

 past season that, although a heavy temporary' decimation of the pest 

 is occasioned by heavy rains, many of the washed-ofi" adults may be 

 carried considerable distances in the surface water at these times only 

 to revive upon stranding and to establish new colonies remote from the 

 scene of their rearing. Thus rains, which for decades have been 

 accepted unchallenged as an unmitigated blessing to mite-infested 

 crops, are, in the light of this recent discover}', to be held equally 

 responsible for potential powers in quite the opposite direction. The 

 composite effect of these opposed economic rain factors is, doubtless, 

 that of greatly decreasing the percentage of infestation while at the 

 same time considerably extending distribution. 



The effect of freezing weather has been previously touched upon. 

 From observations made during the winter, it is doubtless true that 

 most of the mites in the young stages are killed by the minimum 

 temperatures. This naturally prevents any considerable winter 

 increase, and, in addition, a very small percentage of adults may also 

 perish. It must be borne in mind, however, that the red spider is 

 remarkably adapted to withstand low temperatures. To illustrate 

 this point it is interesting to record an observation made at Washington, 

 D. C, during the severe winter of 1911-1912. Adult red spiders 

 collected on a morning following a night temperature of —13° F. were 

 brought into the indoor atmosphere whereupon the majority of them 

 rapidly revived. 



In the case of each of the seasons 1911, 1912 and 1913, during which 

 the red spider has been under observation at Batesburg, a sudden 



