DEFENSES OF BURROWING SPIDERS. 



189 



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DEFENSES OF BURROWING SPIDERS.* 



By HENRY C. McCOOK, D. D. 



1HE simplest form of burrow is that of the Tarantulas, which 

 represent the largest known spiders. These huge araneads 

 appear to depend wholly upon their size to resist the assaults of 

 enemies who invade their den. At least I have not found satis- 

 factory evidence that they erect any artificial barrier over the 

 entrance to their tunnels. 



A more complicated burrow, and one better serving for defense, 

 is that of Leptopelma cavicula of northern Africa. The drawing 

 (Fig. 1) shows a section view of the upper part of the burrow, the 

 entrance to which is without any door or other defense as in the 

 case of the tarantulas. .-,. 



The burrow descends 10: ' 



perpendicularly for a 

 little way, but at the 

 top a special branch di- 

 verges laterally, which 

 curves and again de- 

 scends perpendicularly 

 for a considerable dis- 

 tance. At the summit 

 of this second and par- 

 allel perpendicular tube 

 another branch issues, 

 inclining upward to- 

 ward the surface. A 

 glance at this structure, if we suppose it to be characteristic 

 of the species, and not an accidental formation, will show that 

 it makes an admirable protection against heavy rains, which 

 sink away into the first burrow as a kind of reservoir, enabling 

 the spider to escape by the diverging branch. Against enemies 

 who pursue it into its den, this structure also presents an effect- 

 ual defense, for, while an enemy naturally would rush down- 

 ward into the first direct passage, the spider may escape by the 

 lateral branch. Supposing that the enemy, observing the mistake, 

 ascends and follows along the branches, the spider has the oppor- 

 tunity to push up into the second branch while the pursuer, again 

 following its natural instinct, would rush down the second per- 

 pendicular tube. I am here in the region of conjecture, but per- 

 haps no better explanation presents itself. 



* Reprinted from Vol. II of American Spiders and their Spinning-work, by the kind 

 permission of the author, to whom we are also indebted for the accompanying illustrations. 



Fig. 1. Burrow of Leptopelma camexda. 

 of upper part. 



Section view 



