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IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
Many people have been badly poisoned by standing around 
camp fires on which poison oak branches had been carelessly 
placed. Again after being once affected with the poison of this 
plant, instead of becoming immune from further attack, one 
becomes more susceptible than before. At least this is the tes- 
timony that I have heard so often from friends who have been 
poisoned. 
During the summer of 1915, I undertook a survey of the 
arthropods attacking the poison oak, and after continued search 
over large areas in western Oregon found only a single species 
that was generally distributed and found to be commonly feeding 
on this poisonous plant. This species was a gall mite. Besides the 
gall mite two other arthropod species were listed; the common 
spider mite Teiranychus telarius Linn., and a leaf-roller. In 
this paper I shall report only on the mites, as the leaf-roller 
certainly was not a normal feeder on the poison oak, as neither 
full-fed nor live caterpillars were found. 
The gall mite found on the poison oak was widely distributed, 
and produced very conspicuous, reddish pouch galls on top 
of the leaves (see figure 52). These galls were at times so nu- 
merous that they ran together giving a “cock’s comb” effect. 
Upon dissection the galls were found to be thickly erinosed on 
the inside, and each had an opening on the under surface of 
the leaf. Among the hairs of the erineum were found many 
gall mites of various sizes; some were females with eggs; and 
free eggs also were found inside of the galls. A technical de- 
scription of the mite is here given : 
Phyllocoptes toxicophagus n. sp. 
Capitulum prominent, extending to the end of segment 111 
of leg I. Shield covering cephalothorax. Dorsal setae about 
equal in length to dorsal shield. Abdomen curved downward 
considerably toward the tip, with from 36 to 45 dorsal half 
rings. Lateral setae prominent, equal in length to second pair 
of legs. Ventral setae I reaching over half the distance from 
the point of their origin to the tip of the abdomen, and extending 
to the bases of ventral setae II. Second ventral setae almost 
half as long as the first setae. Legs subequal. Third segments 
of first pair of legs each bearing a long seta which reaches to 
the tip of tarsus. Plumose tarsal setae, each with four pairs 
of bars. Length of male, 140 v - ; width, 50 A Length of female, 
160 f 1 ; width, 60 A 
