DIV.INSECTS 
UNITED STATES DEPARTMENT OF AGRICULTURE 
FARMERS’ 
BULLETIN 
WasHINGTON, D. C. aha JUNE 12, 1916 
Contribution from the Bureau of Entomology, L. O. Howard, Chief. 
THE RED SPIDER' ON COTTON AND HOW TO 
CONTROL IT. 
By E. A. McGrecor, 
Entomological Assistant, Southern Field Crop Insect Investigations. 
INTRODUCTION. 
By the adoption of the preventive measures described in this bulle- 
tin it is possible to avoid the losses caused by the so-called red spider 
(fig. 1), a minute creature which seriously injured 20,000 acres 
of cotton in South Carolina in 1912, and is similarly destructive in 
other Southern States. Injury by the red spider in cotton fields may 
occur from the middle of June until the middle of September. It 
consists in a rusting and dropping of the leaves and sometimes in the 
death of the affected plants over considerable portions of the fields. 
For many years this trouble has been called “ rust ” by cotton planters, 
who concluded from the reddening of the leaves that it was a disease. 
The injury, however, is caused by the presence on the cotton leaves 
of multitudes of small mites called “ red spiders.” 
GENERAL APPEARANCE AND NATURE OF DAMAGE. 
The presence of the pest is first revealed by the appearance on the 
upper surface of the leaf of a blood-red spot. As leaves become more 
infested they redden or turn rusty yellow over the entire surface, 
become folded, then turn brown and dry, and finally drop. The lower 
leaves usually are first attacked, but infestation spreads upward until 
often only the bare stalk and one or two terminal leaves remain. 
(See figs. 2,3, and 4.) Such plants almost always die. 
1 Tetranychus telarius L., generally known as T. bimaculatus Harvey, and in some pub- 
lications as 7. gloveri Bks.; order Acarina, family Tetranychidae. 
38490°—Bull. 785—16 
