SB 
818 
C578 
ENT 
CIRCULAR No. 104. Issued January 26, 1909. 
United States Department of Agriculture, 
BUREAU OF ENTOMOLOGY, 
L. O. HOWARD, Entomologist and Chief of Bureau. 
THE COMMON RED SPIDER. 
(Tetranychus bimaculatus Harvey.)@ 
sy I. H. CHITTENDEN, Sc. D., 
In Charge of Truck Crop and Special Insect Investigations. 
INTRODUCTORY. 
One of the most troublesome of greenhouse pests is a minute, red- 
dish, spiderlike creature, known popularly as “red spider.” It does 
very considerable damage in flower and vegetable gardens, and in 
greenhouses attains its greatest destructiveness. It is particularly 
injurious to violets and roses, and attacks a great variety of other 
plants, including shade and fruit trees and some field crops. Beans, 
cowpeas, senaeee cucumber, and tomato, especially when grown 
in hothouses, sustain much injury, while melons, squash, and berries 
are subject to destructive attack. 
Red spiders are not true insects, in fact not even spiders, but are, 
inore properly speaking, spinning mites. Since, however, they are 
almost universally known as “ red spiders,” this term is retained. 
As the word “mite” indicates, these insects are extremely minute, 
and when they occur in ordinary numbers are not apt to be noticed 
unless the leaves are carefully scrutinized. Attention, however, is 
certain to be drawn to them when they become excessively numerous, 
as frequently happens in neglected greenhouses or out of doors during 
droughts in summer. 
%ed spiders spin threads, but do not, like true spiders, utilize them 
for climbing or for descending from a height. The threads spun are 
extremely fine and scarcely perceptible to the unaided eye, but a web 
@ Until the year 1900 the common red spider, most often occurring in green- 
houses, was technically designated as Tetranychus telarius L., a name whic h 
has been rather indiscriminately applied to all species of red spies) “both: iY, 
America and abroad. 
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