516 THE AMERICAN NATURALIST [Vol. XL VII 



northward and eastward. There seems to be no reason 

 to doubt that the species is multiplying and spreading, 

 for I have it on good authority that in the regions where 

 it is now most plentiful it was almost unknown 20 years 

 ago. Its range is, however, strictly circumscribed by 

 definite ecological conditions as I shall proceed to show. 



Ecology and Habits 

 The armadillo spends its life on the defensive and its 

 defensive equipment consists of structural and func- 

 tional adjustments to a very special environment. Of 

 the structural adaptations the armor (Fig. 1) is the most 

 obvious, but its use is not what it is commonly supposed 

 to be. While the carapace doubtless serves partially to 

 protect the animal when it is attacked by large car- 

 nivors, the fact that dogs often bite through the bony 

 plates and seriously damage the shell shows that for this 

 type of enemy the protection is very inadequate. In 

 fact it is the experience of hunters that, when closely 

 pressed by dogs, the harassed animal turns on the back 

 and strikes most effectively with the powerful claws. 

 The armor has a much more important significance in 

 that it enables the animal to invade the dense, thorny 

 thickets of cactus and chapperal, etc., that characterize 

 its normal habitat. When pursued it is possible for the 

 armadillo to plunge headlong into a mass of thorny 

 vegetation that would be totally inaccessible for an un- 

 armed enemy. Then too they can penetrate all sorts of 

 underbrush in search of insect food without danger from 

 thorns or spines. In some regions of the country the 

 animals take advantage of the rough and rocky char- 

 acter of the hillsides and river banks, seeking shelter 

 from enemies by retreating into holes and crevices among 

 the rocks that are just large enough to admit them but 

 too small for their enemies. Armadillos living in these 

 regions have the armor much worn from rubbing and 

 scraping against the angles and sharp edges encountered 

 in the rocky passages of their retreats. If one is able to 



