HABITS. 15 
In the case of soil, the lumps and sand interfered greatly with prog- 
ress and were responsible for many changes in direction. The dis- 
tance gained by these mites in 10 hours varied greatly, approximat- 
ing 1 to 60 feet from the starting point. The actual distance traveled 
over soil may in some cases exceed the above where the soil is very 
smooth and hard, but on rough ground is probably much less. 
From the foregoing experiments it seems probable that the mites can 
travel some distance over the bare soil, thus infesting plants more or 
less widely removed from those on which they passed the winter. 
EMERGENCE FROM HIBERNATION. 
First appearance of mites on hops. — The hopvines in yards that were 
known to be infested during 1910 were frequently inspected for mites 
during the following spring. The first mite observed upon a hopvine 
was found April 21 in the center of a yard near Sacramento. This 
lone mite was surrounded by eight eggs and protected by a small 
amount of dusty web. No more mites were observed until May 9, 
when a single mite was discovered on a hopvine situated 100 feet from 
a fence dividing two large hopyards near Perkins, Cal. Mites were 
later found upon some early hops which were growing along a fence 
and were also present in about the same numbers upon hopvines some 
distance from the borders of the hopyards. The mites gradually 
increased in numbers, and by June 1 occasional hopvines were found 
on which the lower leaves harbored from 5 to 33 mites each. 
As is shown by the foregoing data, the mites appeared simultane- 
ously in various parts of the hop fields and did not, as was formerly 
supposed, invade the yards from along the edges and work toward the 
center of the fields. 
MIGRATORY ACTIVITIES. 
Before the infestation became severe the mites were observed upon 
the underside of the lower leaves, over which they had spun a small 
amount of web. No distinct migration was noted at this time, but 
as the mites increased in numbers the infested leaves were seriously 
injured and partially dried. In this condition they furnished very 
little food and forced the mites to migrate to fresh foliage, leaving 
behind them from 100 to 450 eggs and at least one-tenth as many larvae. 
Gradual upward migrations continued until the last of July, at which 
time the plants were entirely infested. 
During the month of August a new condition was observed. The 
morning-glory in the hopyards had become seriously injured by 
mites. A migration caused by the sudden decrease in the food supply 
was begun and soon became very extensive. Myriads of mites were 
seen crawling from the dying morning-glory, over the clods, up the 
vines and trellis poles, and covering everything with a fine web. 
A similar condition was noticed on a few hopvines that had fallen 
from the wire. The leaves that were farthest from the ground were 
-74955°— Bull. 117—13 3 
