326 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
The other mite found feeding on the poison oak is no other 
apparently than our common Teiranyckus telarius Linn., or 
spider mite. It differs from most of the forms of this variable 
species in being smaller, and in never being orange in color. 
This species was found in only one place, in a pasture inside of 
the city limits of Corvallis, Oregon, but was found here some- 
what in abundance. The infested leaves were somewhat paled 
and cupped, but not seriously injured. On their undersides 
were found many mites, including males and females in about 
equal abundance ancl some eggs. 
What do we know of the host distribution of these two spe- 
cies? The gall mite, Phyllocoptes toxicophagus sp., is, as 
far as we know restricted to tlie poison oak. The spider mite 
is found on many kinds of plants throughout the most of North 
America and Europe. Recently I compiled a list of seventy- 
eight species of plants belonging to many families, on which this 
mite had been recorded as feeding. It is in fact almost omniv- 
orous. We have in this case, therefore, a species that is espe- 
cially noted for its hardiness, its wide distribution, and its 
varying food habits feeding on a poisonous plant. But liow 
about the gall mite? Here it is possible that the mite species 
itself became so adapted that it could withstand the toxin, so 
deadly to most species. But could it not be that this gall mite 
has been evolved along with its host species? Could it not be 
that the parasitic habit was established on an ancestor of the 
poison oak that did not possess the poisonous properties, apd 
that the mite has persisted ever since as a parasite on succeed- 
ing generations of hosts? I see no reason why the latter sug- 
gestion js not a logical one. 
Zoology Department, 
Iowa State College. 
