THE TARANTULAS 113 



strengthening its closed tube, it is less subject to the attacks of 

 marauding wasps that, in order to satisfy the food requirements of 

 their offspring, pass up the smaller burrows in favor of mature or 

 nearly mature prey. 



We pass now to consideration of the three better-known 

 types of trap-door spiders found in the United States. The first of 

 these constructs the classical type of nest that Moggridge called the 

 "cork nest." The most familiar domicile of this type is made by 

 Bothriocyrtum calif ornicum, the common trap-door spider of south- 

 ern California. Examples of this nest (Plate XI) are to be found in 

 many collections, and may even be purchased from various biologi- 

 cal supply houses. It is the typical nest illustrated in many works 

 on natural history. Another group of spiders that is widely dis- 

 tributed across the southern United States, the genus Pachylomerus, 

 also makes this type of nest. These spiders are very handsome 

 animals, with a nearly oval, black, shining cephalothorax and legs, 

 and a dusky abdomen. 



The cork nest (Text Fig. 3, A) is a simple tube without side 

 branches, lined completely with silk. Ordinarily the burrows are 

 shallow, from five to eight inches in depth, with a diameter essen- 

 tially the same throughout and great enough, especially near the 

 entrance, to permit the spider to turn around. The distinctive fea- 

 ture of this nest is the door (Plate XI). It is made of layers of earth 

 and silk, and is so constructed that it fits perfectly and tightly closes 

 the mouth of the tube "much as a cork closes the neck of a bottle" 

 so Moggridge described it. The cork door cannot stand open; it 

 falls and closes of its own weight, and the tube mouth is beveled to 

 receive it. 



In West Florida Pachylomerus audoumi digs its burrows in the 

 sides of steep, stream-cut banks in moist and shady ravines. Ari- 

 zonan and Mexican Pachylomerus favor open spaces in the sun- 

 baked creosote-bush deserts. In southern California Bothriocyrtum 

 californicum makes its tunnels on sunny hillsides that in early 

 summer bear a thick covering of native grasses. The spiders that 

 build the cork nest are plump animals (Plates XII and XIV) with 

 rather short legs and a broad carapace. They are the finest bur- 

 rowers, and have, in addition to the well-developed cheliceral rake, 

 rows of short digging spines on the first legs, which aid in scraping 

 and cutting the soil. Their bodies are rounded and fit the burrow 

 snugly, with the legs pressing closely against the sides. Their struc- 

 ture bespeaks strength and ruggedness. As is true of most spiders, 



