A BIRD'S NEST, AND OTHER ANIMAL HOMES 39 



larvae hatch, their wrigghng and feeding irritate the sen- 

 sitive tissue so that it grows in an abnormal way and 

 forms a gall, often very large, about the insects. 



All these burrows and galls may be looked on as the 

 simplest kinds of houses or homes, the young insects 

 living in them, and being protected by them. 



Most spiders spin silken cocoons (fig. 21), or sacs, in 

 which to deposit their eggs. Some spiders carry this 

 egg-filled cocoon (fig. 22) about with them for the sake 

 of protecting the eggs. After hatching the spiderlings 

 remain in it a short time, feeding on each other ! Thus 

 only the strongest survive and issue from the cocoon to 



Fig. 22. — A female running spider {Lycosidtt) carrying its egg-sac about 

 attached to its spinnerets. (From Jenkins and Kellogg.) 



earn their living in the outer world. With certain species 

 of spiders the young after hatching leave the cocoon and 

 gather on the back of the mother and are carried about 

 by her for some time. In connection with their webs 

 or snares many spiders have silken tunnels or tubes in 

 which to lie hidden, a sort of sheltering nest. Those 

 that live on the ground make for themselves cylindrical 

 burrows or holes in the ground, usually lined with silk, 

 in which they hide when not hunting for food. Espe- 

 cially interesting among these many kind of nests are the 

 burrows of the various trap-door spiders (figs. 23 and 24). 

 These spiders are common in California and some other 

 far Western States. Their burrow or cylindrical hole is 

 closed above by a silken, thick, hinged lid or door, a little 

 larger than the hole in diameter, and neatly beveled on 

 the edge, so as to fit tightly into and perfectly cover 



