18 BULLETIN 416, U. S. DEPAETMEISTT OF AGEICULTUEE. 



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 defohated. If the 

 progress of the pest is checked, through natural conditions or by 

 spraying, the health 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 abiUty of these creatures to construct webbing. 

 There is stiU 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 during 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 



