ENEMIES AND THEIK INFLUENCE. 407 



in about six weeks, when it at once begins to feed upon tbe stored spider. 

 When full grown it passes into a chrysalis state, in which it remains until 

 the following summer, when it emerges, a mature insect, and, like its 

 mother, begins a remorseless raid upon the Tiger spiders. The wasps con- 

 tinue their raids for two or three weeks, only the spiders with closed 

 doors escaping. Sometimes a spider will keep herself shut up for two 

 weeks and then timidly open her door and look out. 



After the end of August the maternal rage had exhausted itself, the 

 wasps disappeared, and then Mrs. Treat found that out of twenty-eight 

 spiders only five were left ! These survivors soon opened their doors, and 

 occasionally one would cut the threads of the spinningwork which unites 

 the thatching material in such a manner as to make a sort of trapdoor, 

 leaving hinge on one side. (See Figs. 341 and 342.) But more commonly 

 a hole was left in one end of the oven shaped cover, which the spider 

 would readily close by drawing the material together and fastening it with 

 threads. 



It seems impossible, in view of such a careful and intelligent record 

 as this, to doubt the fact that the instinct by which Lycosa tigrina is im- 

 pelled to construct the vestibule roof and door to her den, has 

 Danger b een vitalized by, or at least associated with, the natural in- 

 , , . stinct of self protection against the raids of its formidable enemy, 

 the Digger wasp. This is further emphasized by the fact that 

 the partly grown Tigrinas, who are not molested by the wasps, have never 

 been observed to conceal their burrows in the manner of the adult. Tigri- 

 na's rude architecture is a product of her peril. 



The defensive motive in the architecture of Lycosa tigrina, which is 

 thus clearly demonstrated, serves as a key to the purpose underlying all 

 the architecture, not only of the Lycosidae, but of other burrowing spe- 

 cies. The watch tower which guards the nest of the Turret spider (Vol- 

 ume I., Fig. 289, page 314) ; the interesting structure so closely resembling 

 a bird's nest, reared above her nest by Lycosa carolinensis (Volume I., 

 Fig. 291) ; and other forms of industry of which these are types, may all 

 be considered as in part, at least, the result of protective industry. 



According to the account of Dufour, the habits of Lycosa tigrina and 



Lycosa arenicola are quite similar to those of the famous Lycosa tarentula 



of Italy, the heroine of the " Tarentula dance." This aranead 



ycosa f orms a cylindrical burrow in the earth, often more than a foot 



long, and about one inch in diameter. At about four or five 



inches below the surface the perpendicular tube is bent horizontally, and 



it is at this angle that Tarentula watches for the approach of enemies or 



prey. The external office of the burrow is ordinarily surmounted by a 



separately constructed tube. This tube and outer piece of architecture 



rises about an inch above the surface of the ground, and is sometimes as 



much as two inches in diameter, being thus even larger than the burrow 



