Circular No. 1 50. 



Issued April 25, 1912. 



United States Department of Agriculture, 



BUREAU OF ENTOMOLOGY, 

 L. O. HOWARD, Entomologist and Chief of Bureau. 



THE RED SPIDER ON COTTON/ 



{Tetranychus himaculatus Harvey.) 

 By E. A. McGbegob, 

 Sdentiflc Assistant. 



INTRODUCTORY. 



The minute, reddish spinning mite commonly known as the red 

 spider is rapidly assuming a position of importance among cotton 

 pests. At Batesburg, S. C, in 1911, it 

 first became noticeable on cotton about 

 June 1, causing little more than passing 

 notice at that time among the farmers, 

 but by the 1st of July it had increased so 

 enormously that the effect upon cotton 

 in certain places was most alarming. 

 Seasons of excessive drought greatly fa- 

 vor the multiplication of the mites until 

 the resulting injuries are often so severe 

 as to cause the death of many plants. 



Red-spider infestation is frequently 

 miscalled " rust " by farmers, since in- 

 fested leaves soon turn deep red on their 

 upper surface. Such leaves, however, if 

 examined underneath, reveal the pres- 

 ence of the red spiders and the incon- 

 spicuous webs behind which they are 

 feeding and laying their eggs. 



HISTORY AND DISTRIBUTION. 



Fig. 1. — The red spider, Tet- 

 ranycJius bimaculatiix: Adult 

 fomalp. Greatly enlarged. 

 (From Banks.) 



With the exception of an outbreak in 

 Louisiana, reported by Prof. H. A. Mor- 

 gan in 1893, severe occurrence of tlie cotton red spider had not 

 been reported until 1903, at which time complaints of damage came 



1 This circular is based primarily upon work done at Batesburs. S. C, in 1911, 

 under the direction of Mr. W. D. Hunter, but also includes the results of observations 

 by Messrs. G. .V. Runner and H. F. Wilson during the two preceding seasons. 



