69 
to the leaf and to the eggs. The mites walk about without using 
them. As the leaf curls by loss of juices the threads become more 
separated from the leaf, so that some mites are under and some on the 
web, which seems to be in their way. Since the thread seems to be 
of use at first in keeping the eggs in place, it may be that it issues 
from the genital opening at about the time of oviposition. 
HABITS. 
Attention is usually drawn to these mites when they become excess- 
ively numerous during a drought in summer. Little is known about 
the other portion of their 
lives. They are sup- 
posed to pass the winter 
in the adult condition 
under and among dead 
leaves; in the spring 
ascending trees and start- 
ing new colonies. It is 
quite probable that only 
females hibernate; if these females have not been fertilized the first 
egos they lay produce only males, which when adult will pair with 
the females, and the latter will then lay eggs producing both sexes. 
Various observations have been made on the rapidity of their increase. 
The general results are that the female lays from five to ten eggs per 
day for a period of eight to twelve days; the eggs hatch in about two 
to seven days (three days is probably the most common period); the 
young at first have but six 
legs; after a few days they 
molt and have eight legs; two 
more molts occur a few days 
apart, and then they are adult. 
Their movements are ordi- 
narily slow, but when dis- 
turbed they sometimes stir 
quite rapidly. Forthe greater 
Pe macs wsecosh commer fam" part of the time they remain in 
much enlarged (original). one place sucking the juices 
from the leaf. But migration 
is probably not wholly dependent on food supply, since plants are 
found scantily infested in various parts and the mites are not abundant 
anywhere. Although they spin threads they have never been ob- 
served to hang by or climb up one. The thread is extremely fine and 
not perceptible to the unaided eye. Yet a web or mesh of threads is 
so dense as to form a tissue plainly visible at a considerable distance. 
The web is usually upon the under side of the leaf, attached here and 
Fia. 5.—Tetranychus: genital organs—highly magnified (origi- 
nal). 
