AGRICULTURAL EXPERIMENT STATION. 137 



yield to the same treatment. If the specimens sent us by Dingee 

 & Conard Co. and Prof. Bailey's men, were the genuine red 

 spider, we are forced to conclude that in this mite we have a 

 species scarcely sepai'able from the red spider by its structure but 

 differing very much from it in habit. If called upon to decide 

 from the structure alone we would be compelled to call it a form 

 of the polymorphous species Tetranychns telarius, L., or red 

 spider. 



No importance can be attached to color in this species nor in the 

 red spider for in both it is variable with the food plant and also 

 with the age, each molt disclosing a different shade. All we have 

 left upon which to construct this species is the marked physiological 

 differences, noted by Henderson, Bailey and Munson. Can it be 

 possible that it is a case of adaptability — a form of the red 

 spider that has changed its mode of living to suit new conditions ? 

 Such cases are not uncommon among insects. We leave it an 

 open question for a want of sufficient data. The published 

 descriptions and figures of the red spider are so meagre and so 

 lacking in minute detail that it would be very difficult to determine 

 from them whether specimens in hand belonged to that species. 

 Even the published characters of the genus Tetranychus are 

 faulty on account of imperfect microscopical examination. 



General Description. 



Perfect insect — length of full grown specimens, including pal- 

 pus, .4 to .6 mm.; breadth, .25 to .3 m m. ; thickness .175 to .2 

 m m. Broadly oval, about two thirds as broad as long. Broadest 

 in the anterior third of the body back of the eyes, where the sides 

 are somewhat swollen. General color when joung or free from 

 food, pale orange or greenish yellow, becoming yellowish orange 

 or orange with age. The majority of the specimens have a dark 

 spot on each side as shown in Fig 1. due to food contents. These 

 spots first appear, in young specimens which have six legs, as 

 scattered brownish or greenish spherical bodies that look like oil 

 drops. These increase in number with age and are sometimes 

 arranged in three groups. Finally they merge into a single mass 

 as shown in Fig. 1. In older specimens dark patches are found 

 in the anterior and posterior portions of the body, (see Fig. 2), or 

 in full fed specimens the body is entirely dark colored. The 

 shade seems to vary with the color of the food, from the yellow 

 orange and brown to green, dark green or black ; those feeding 

 on calla, especially, a deep dark green. 



