down like a bristly Gulliver by multiple tiny bonds. 



The fact that Loretta was able to break her eighty- 

 four connections in a flash suggests something is 

 wrong with my analysis. David M. Chapman, a his- 

 tologist at Lakehead University in Thunder Bay, 

 Ontario, who has studied porcupine skin and quill 

 follicles microscopically, offers an alternate explana- 

 tion: the force needed to separate a quill follicle from 

 the skin of the porcupine may drop after the quill 

 has been driven into an adversary. Consider one of 

 the quills stuck in my rubberized glove. When the 

 quill tip struck the glove, an equal and opposite re- 

 active force drove the quill root deeper into the skin 



of the porcupine. The inward push was probably vi- 

 olent enough to break some of the attachments be- 

 tween the base of the quill and its surrounding tis- 

 sues. As a result, less force would have been needed 

 to separate the quill from the porcupine's body 



How to test the hypothesis? Pulling quills from 

 a porcupine on the defensive is difficult and 

 dangerous business. Chapman suggests an elegant 



Threatened by a predator, a porcupine (above) hunkers down with 

 its head away from the danger, preparing to use a slap of its tail to 

 thrust sharp-pointed quills into its enemy (dog at right). To avoid a 

 full-blown confrontation, the porcupine also emits a highly distinctive 

 and pungent odor, warning its foe to back off. 



way around the problem. Strike the back of an 

 aroused porcupine with a block of something light 

 and penetrable, such as cork or styrofoam, and leave 

 it in place. Then anesthetize the animal, separate the 

 block from the animal by cutting off the tips of the 

 quills embedded in the block, and measure the force 

 needed to pull the quills with the cut-off tips out of 

 the animal's skin. 



I try the technique on a female I have named Heart. 

 The results are clear-cut: it takes, on average, only 1 .9 

 ounces per quill to pull the six struck quills out of the 

 animal. By contrast, it takes 3.4 ounces per quill to 

 pull six undisturbed quills from the same area on the 

 porcupine. Experiments with other porcu- 

 pines confirm that the tension required to ex- 

 tract a quill from a porcupine is reduced by 

 about 40 percent if the quill is first driven 

 into the porcupine's body. That's exactly 

 what would happen after a tail slap or other 

 violent contact with an antagonist. 



Chapman has photomicrographs that 

 show enough detail to figure out how the 

 trick is done. Beneath the surface of the por- 

 cupine's skin, each quill is surrounded by a 

 spool-like structure made up of dense con- 

 nective tissue [see illustration on opposite page] . 

 This "guard spool" lies just below the shoul- 

 ders of the quill shaft, which flare outward 

 sharply and so prevent the quill from being 

 driven deep enough into the porcupine to 

 cause the animal injury. 



When the porcupine is relaxed, the guard 

 spools move freely: if you strike the quills of 

 an anesthetized porcupine, the spools just 

 glide in with the impact, and the quills remain 

 anchored in the animal as firmly as ever. (That 

 property guarantees, for instance, that a sleep- 

 ing porcupine doesn't lose its quills if they ac- 

 cidentally press against a tree trunk.) When a 

 porcupine is provoked, however, and its quills 

 are erect, the guard spools are held in place by taut 

 connective tissue in the skin. If a strong downward 

 force is applied to the quill's shaft, it drives the quill 

 root deeper into the porcupine and shears it from the 



50 NATURAL HISTORY March 2006 



