THE BED SPIDER ON COTTON. 29 



Rate oj travel. — In order to ascertain . the rate of movement of 

 wandering red spiders a series of laboratory experiments was con- 

 ducted. A large sheet of coarse wrapping paper was fastened tightly 

 on a 4 by 6 table. The red spiders to be tested were liberated at the 

 center and their progress was traced for periods varying from 5 to 

 90 minutes. 



The influence of temperature on the rate of travel was very marked, 

 and was established by conducting the foregoing tests on both hot 

 and cool days. It also develops that the average rate of travel by 

 the female red spider in summer is 4.82 inches per minute, while that 

 of the male under similar conditions is 2.95 inches per minute. (See 

 Table IV.) 



SOURCES OF DISPERSION, 



When cotton fields occur in urban localities it often happens that 

 infestations arise directly from garden or dooryard plants, such as 

 the violet, sweet pea, dahlia, hollyhock, garden bean, etc. (PI. IV, 

 figs. 3-5; PI. V, fig. 4.) As has been pointed out, however, the pest 

 more usually reaches cotton in the course of a series of migrations, 

 beginning with the primary hosts as foci, and advancing from host to 

 host as the native species appear above the ground in spring. The 

 plants which so happen to harbor the pest in situations adjacent to 

 cotton, when the latter appears, become the immediate sources of 

 dispersion to the cotton field. 



Weed borders (PL V, fig. 5), which have been known to give rise 

 to very acute infestations in adjoining cotton fields, and which pre- 

 vail throughout the entire year, have been made the subject of con- 

 tinued observation, with the result that the position of such weeds 

 in the problem is now quite clearly miderstood. There are certain 

 weed species that at times occur in almost pure growths; that is, 

 countless thousands of seedlings of a given species may grow in con- 

 tinuous, dense borders. This was often noticed at Batesburg, where 

 at times weed infestation became so acute that entire borders of 

 Geranium carolinianum, Stachys arvensis, etc., wilted, and finally 

 succumbed entirely. It is just such cases as these that produce a 

 migration of red spiders to the cotton fields. A rather complete list 

 of the native plants at Batesburg which arc of great importance in 

 advancing the red spider to cotton in the spring is given in Table V . 



