THE EED SPIDER ON COTTON. 19 



heavily infested plants it may occur on all parts of the host, the whole 

 apical portion of the plant having a silvery appearance. 



There has been considerable conjecture concerning the function 

 of the webbing. The surface of the leaf is preferred for oviposition, 

 and it is apparently only when overcrowding has resulted in a con- 

 fusing maze of fibrils that the females resort to the webbing as a 

 medium upon which to place the eggs. Hundreds of mites in 

 experiments have been observed to molt or to prepare to molt, and 

 without exception they have fixed themselves for the quiescent 

 period directly upon the surface of the leaf. 



It has been thought by some writers that the travel of red spiders 

 is facihtated by the presence of the web and that travel upon cer- 

 tain hirsute plants is practically impossible without the aid of web- 

 bing. In our work mites have been seen crawling readily over the 

 surfaces of aU sorts of pubescent and hirsute plants which possessed 

 no trace of webbing. We have tested larvae, nymphs, and adults on 

 the pilose surface of velvet and find that they travel readily over the 

 innumerable projections of the pile. 



The suggested aerostatic role of the webbing in conveying mites 

 through the air seems improbable. We have never seen web appear- 

 ing as though damaged by wind, and neither in the experiment by 

 Mr. E. E. Munger during 1912 in California on wind dispersion nor 

 in those of a similar nature conducted at Batesburg has a trace of 

 web been detected on the screens coated with a sticky substance, 

 although many red spiders have been thus taken. 



We believe that the function of the webbing is that of protection. 

 Among the agencies against which this protection undoubtedly serves 

 are: Spattering raindrops; upward bombardment of soil particles 

 during heavy storms; jarring of foliage caused by driving storms, 

 wind, or sudden contact; flooding, in the case of prostrate plants; 

 the attack of predatory insects, etc. We have often examined infested- 

 leaves the undersides of which were heavily coated with soil par- 

 ticles, and after carefully removing the web found the mites unin- 

 jured and active behind the protective canopy. On other occasions 

 following heavy downpours leaves not supplied with webbing have 

 frequently been observed completely freed of the red spider, whereas 

 leaves bearing webbing, although subjected to the same storms, 

 still retained a great many mites. Again, low, prostrate plants 

 have frequently been examined following flooding rains and the low- 

 est leaves often found to be heavily coated beneath with a deposi- 

 tion of scum that had bo(!n hsf t upon the retreat of the surface water. 

 In such cases, when web had intervened between the mites and the 

 water, the creatures surviv^fid the flooding and could be found pur- 

 suing their various activities without sc^rious im pediment. 



