INSECTS. 107 
spider, living under rocks and in holes in the ground, which 
they often excavate to a depth of nearly.a foot, lining the 
sides with silk, and covering the opening with a scaffold- 
ing of mud and wood cemented together. The Zarantula 
nidifex erects a tower over its tube, the foundation-pieces 
of wood selected being generally the exact shape of the 
hole. These are piled one upon another precisely as the 
woodsman builds his log-cabin, until a regular chimney is 
the result. TZ. turricula (Treat) (Fig. 127) erects a some- 
what similar tower; the 
female carries the young 
on her back. 
Crab-Spiders (1%- 
gale).—These often meas- 
ure six or seven inches 
across, including the legs. 
They are covered with FIG. 128.—Poison-fang of a spider 
thick, reddish hair, and (Cluétona), highly magnified. 
possess terrible fangs (Fig. 
128). They have four lung-sacs and two pairs of spin- 
nerets, They prey upon birds (Fig. 129) and various 
small animals. ; 
Mygale Henzii is common on our western plains and 
in Utah. Some are called trap-door spiders, from the fact 
that after their well-like nest is excavated they cover the 
entrance with a circular door that works on a perfect 
hinge. The dwelling is generally formed in gravelly 
ground, and material moved piece by piece, until finally a 
well is sunk perhaps a foot deep. To prevent the sides 
from caving in, the spider now covers them with a coat- 
ing of silk, so that the interior presents a perfectly smooth 
surface. The door is formed of various material, all 
wound about with silk in a firm, flat, oval mass, the spider 
whirling itself about in the operation, finally producing a 
door attached to one.side by a silken hinge that fits ex- 
actly, even keeping out water, and is so adjusted that it is 
