ENEMIES AND THEIR INFLUENCE. 403 



their whole life is spent in a defensive industrial warfare for the protec- 

 tion of their persons. In order to illustrate this truth a little more fully 

 I propose to consider the habits of those spiders which make burrows in 

 the ground, namely, the Citigrades and Tunnelweavers. Both of these 

 tribes, but particularly the latter, are noted for the admirable dwelling 

 places which they construct. I hope to show that these ingenious homes 

 are largely defensive. 



Beginning with the Citigrades, we find, in the first place, that during 



the period of moulting, when the spider is conscious of its de- 



. ' u " fenseless condition by reason of physical weakness, it is in the 



habit of protecting itself by covering the mouth of its den with 



a silken sheet, or by spinning a special cell in which to shed its skin. 



Again, I have observed Lrpcosa, when about to make her cocoon, con- 

 struct a cell in the earth and carefully cover the entrance thereto with a 

 silken curtain. She was animated, as I conjectured, by the wish to pre- 

 serve herself from enemies during this crisis period of her life. I have 

 also shown that it is the universal habit of these Lycosids to construct co- 

 cooning caves or nests underneath stones, logs, and like situa- 

 tions, which are carefully plastered and enclosed on all sides. 

 cooning f 



Caves leaving an entrance which is usually well protected from assaults 

 of ordinary enemies. This appears to be a cosmopolitan habit; 

 at least, Mr. Campbell tells us that some English Lycosids dig an irregular 

 oval cavity about one inch by a half inch in diameter, close it with a con- 

 glomerate of silken threads and earth, and remain therein with the 

 cocoon. He kept one Lycosid in confinement and twice destroyed her 

 retreat, only to find another made the following morning. The top was 

 covered with granular pieces of soil, such as might have been raked over 

 the silken lining with her feet. In both the above conditions, namely, 

 while moulting and while cocooning, these Citigrades appear to be driven 

 to special industrial provisions by the impulse of self protection. 



That the same habit prevails as a protection against the destructive 

 influences of climate is well attested. Lycosids everywhere appear to seal 

 up the openings to their cylindrical burrows at the advent of 

 winter. The advantage of such artificial closure, as a protec- 

 Covers. ^ on a g ams t winter cold, was well demonstrated by Mrs. Treat. 

 A large example of Lycosa carolinensis, which makes a beau- 

 tiful nest (Fig. 291, Vol. I., page 316) was brought from New Hampshire 

 and domiciled in Mrs. Treat's ground. Its burrow was only eight inches 

 deep, yet there was a marked increase of temperature above that at the 

 surface. This could be discerned by placing the hand at the mouth of 

 the tube. One cold morning when the thermometer stood twenty degrees 

 above zero CFahrenheit) a thermometer was introduced. It ran up to 

 forty degrees, making a difference of twenty degrees in temperature be- 

 tween that prevailing at the surface and that within the burrow. Soon 



