18 BULLETIN 416, U. S. DEPARTMENT OF AGRICULTURE. 
ruptured and the palisade cells become shrunken and distorted. 
Each incision of the stylets causes a blackish spot, and after much 
feeding the infested leaf becomes thickly spotted underneath. There 
is a change of color in the portions of the leaf attacked which develops 
especially on the surface immediately over the injured area. In 
the early stages of infestation this coloring reveals itself as small 
blood-red blotches, which vary with the number of mites present 
and with the extent of surface attacked. As leaves become more 
heavily infested the entire leaf often becomes involved and the 
effect is soon very marked. The petiole droops to a marked extent, 
and the entire leaf turns rusty red and later becomes brown and dry. 
The lower leaves are first attacked, but infestation spreads upward 
until the plant becomes almost completely defoliated. If the 
progress of the pest is checked, through natural conditions or by 
spraying, the heaith of the foliage is frequently restored and only a 
few leaves may be shed. 
The nature of the injury to plants other than cotton is not mate- 
rially different from that just described. It is not, however, usual 
for most plants to exhibit the red blotching. In the case of garden 
beans, hollyhock, sweet peas, and many other hosts (PI. IV; figs. 2, 
5, and 7) the badly affected leaves assume an ashy hue due to the 
presence of innumerable grayish puncture specks. 
Web spinning—For more than 100 years the red spider and its 
close relatives have been known as spinning mites or ‘‘spinne- 
milbe,’”’ owing to the ability of these creatures to construct webbing. 
There is still uncertainty, however, regarding the nature and location 
of the spinning apparatus, some workers claiming that the glands 
are located near the mouth, while others contend that the threads 
issue from the anal end of the body. Ewing (1914) asserts that the 
silk emerges near the anus and that the four-pronged‘ tarsal claw and 
the tennent hairs, found on the tarsi, are used in its manipulation. 
The fibrils formed by this species are so exceedingly fine that they 
are almost invisible. Many of them together are visible as a silvery 
sheen on the much-infested surface (Pl. IV, figs. 1 and 2). The 
strands are not arranged as a symmetrical web, but merely extend 
from point to point on the leaf, from leaf to stem, or from one leaf 
to another. Under normal conditions it appears that the thread 
is not produced durmg the ordinary wanderings of the mite, but 
becomes elaborated at special times, as when the host becomes non- 
succulent through drought, when the supporting plant becomes 
overrun by the pest, or in the presence of numerous enemies. As 
the leaf curls through the loss of juices the threads become separated 
from the leaf, so that some mites are under and some on the web. 
The web is normally confined to the underside of the leaf, but on 
1 In his description of the tarsus Ewing (1914) describes it as “ divided into six prong-like elements.”’ 
