THE BED SPIDER ON COTTON. 27 



weather are almost certain to perish with the return of lower tem- 

 peratures. 



Variation in ahundance from year to year. — It is noticeable that the 

 degree of occurrence varies greatly from year to year. We find 

 from a study of the various natural influences that it is possible to 

 foretell the probable status of the pest during a given season with 

 considerable assurance. The red spider is extremely resistant to 

 adverse meteorological conditions, and no matter how severe the 

 winter, a considerable proportion of the mites come through safely. 

 On the other hand, many of the insect species which are predatory 

 upon the red spiders, being of a more susceptible nature, are less 

 likely to survive the hardships of a severe winter. Theoretically, 

 after a mild winter there should be am abundance both of mites 

 and predators, while after a severe winter the mites should survive 

 in a much greater proportion than their enemies. This condition 

 has obtained during the past four years, mild winters being followed 

 by mild red-spider seasons, while severe winters have been followed 

 by seasons of heavy mite occurrence. 



DISPERSION. 



When the food supply on favorable host plants becomes exhausted 

 dispersion to new food plants takes place, and it is usually by a 

 succession of such dispersions that cotton finally becomes infested. 



Ground travel. — On many occasions red spiders have been observed 

 crawling on the ground in the vicinity of grossly infested plants, fre- 

 quently crawhng up and down the stems in search of more favorable 

 hosts upon which to feed. In order to ascertain whether red spiders 

 leave the plants of their own vohtion and crawl upon the ground 

 in attempts to extend their range, the following experiment was 

 instituted. 



Tests of red-spider movements. — Large sheets of sticky fly paper 

 were carefuUy fitted about the bases of cotton stalks.- The sticky 

 surfaces were permitted to remain in this position for periods varying 

 from 24 to 48 hours. At the conclusion of these exposures careful 

 examinations were made, of which the following specific results are 

 rather typical: Five red spiders were observed on the inner edge, 

 which came in contact with the base of the stalk; 29 mites were 

 caught on the extreme outer edge, which was flush with the finely 

 packed soil; 5 red spiders were found ensnared at dffferent points 

 in the central area of the sticky surface. The only possible deduc- 

 tion is that the first-mentioned 5 individuals were intercepted as 

 they were desfcnding the stem; that the 29 mites were trapped as 

 they were crawling over the ground surface, presumably toward the 

 cotton stalk; and that the last-mc^ntioned 5 undoubtedly dropped 

 directly from the overhanging foliage. 



