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 Tarantula 

 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. T. turricula (Treat) (Fig. 127) erects a some- 

 what similar tower ; the 

 female carries the young 

 on her back. 



Crab -Spiders (My- 

 gale). These often meas- 

 ure six or seven inches 

 across, including the legs. 

 They are covered with FlG I23 ._ Poison _ fang of a spider 



thick, reddish hair, and (Clubiona), 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, evan keeping out water, and is so adjusted that it is 



