Similarities/differences between the porcupines of different Hemispheres: Erethizon vs Hystrix, part 2

continued from


The colouration of both Erethizon and Hystrix combines

Erethizon differs from Hystrix in that, in the winter coat, the pale surfaces of the spines themselves are generally invisible on the body of the relaxed or normally active figure, being covered by long non-spiny hairs ( and

The colouration of Erethizon is more variable individually, seasonally, and regionally, than that of Hystrix.

However, in Erethizon

In Hystrix, the tail is conspicuously pale, but only in


Both Erethizon and Hystrix base their anti-predator defences on barbed spines, which are much-thickened, fortified hairs with pithy (spongy) interiors ( and

The spines not only pierce the skin of attackers, but detach easily from the source.

This leaves the spines firmly embedded and able to work their way, by virtue of the automatic/passive ratchet-mechanism of the barbs, either

  • perpendicularly, deeper into the body with the risk of penetrating internal organs, and/or
  • laterally and subcutaneously, parallel to the surface of the body.

See and and and and and and and and

The two genera differ in:

  • the length of the longest spines: up to 7.5 cm in Erethizon vs up to 30 cm in Hystrix, and
  • the extent of spininess in the pelage: covering much of the body plus the crown in Erethizon, vs restricted to the back and hindquarters in Hystrix.

The following show the shortness of the spines of Erethizon: and and and and and and and

The following show the lengths of the spines of several species of Hystrix: and and and and and and and and and

When predators eat Erethizon, they discard the whole skin ( In the case of Hystrix, only the pelage itself is discarded, the skin apparently being eaten.

In both genera, the defensive syndrome is accentuated by

However, Erethizon and Hystrix differ in several ways, as follows.

Erethizon seems not to strike until the pelage is touched, whereas Hystrix attempts to strike preemptively once the potential predator approaches closely. Erethizon thus tends to strike as retaliation, whereas Hystrix tends to strike as intimidation. This is consistent with

  • the visual display being starker in Hystrix than in Erethizon, and
  • the defensive display being in a sitting posture in Erethizon vs a standing posture in Hystrix.

Both Erethizon and Hystrix have a large patch of spines on the rump, lacking guard hairs, that is exposed by the erection of the surrounding long pelage. In this rump-patch the spines (which are short in both genera) have mixed orientations ( and and and and and and and and

Only Erethizon uses odour as part of the defensive repertoire, compensating for the limited conspicuousness of the relatively short spines (

This odour is secreted from the otherwise bare-skinned patch of dark spines on the back/rump, and is facilitated by a wick effect of these spines themselves ( and and

The release of the defensive odour is accompanied by a second stage in the activation of the pelage of the rump. In the first stage, what is displayed is a patch of mainly whitish spines. In the second stage, the tone changes to dark, and the warning changes from visual to olfactory.

Only Hystrix uses pilo-erection of long hairs other than guard hairs or spines to exaggerate its body size as part of the defensive display. This produces a 'nuchal crest' ( and and and and and

In Erethizon, the guard hairs on the crown and nape can be long ( and, but there seems to be no particular display of these as part of the anti-predator reactions. Furthermore, the crown and nape - like the rest of the forequarters - are spiny in Erethizon ( and and while lacking spines in Hystrix.

In both genera, the tail bears erectile spines and can have warning colouration:

However, in Erethizon the tail is proportionately large and muscular enough to be wielded as a flexible, fast-moving, spine-embedding organ, and its colouration tends to contrast dark on the upper and lower surfaces with pale on the sides ( In Hystrix the whole tail tends to be conspicuously pale in two of the species (see above). This is fully exposed to view once the long pelage around the rump-patch is erected in the warning reaction (

In Hystrix a main function of the tail (but restricted to certain species) is production of a warning sound - namely a hiss-like rattling - by means of specialised caudal quills. These are broad, hollow, and whitish, but blunt and harmless; in their full development they may have narrow, flexible stalks.

Both genera thus use percussion as part of their defensive repertoire.


  • Erethizon clacks the incisors ( and chatters the cheek-teeth (mainly in males), and slaps the tail on the ground, whereas
  • Hystrix rattles the pelage (particularly the specialised caudal quills), grunts, and stamps the feet.

to be continued...

Posted by milewski milewski, May 02, 2022 13:34


Posted by milewski about 2 months ago (Flag)

Does anyone know if Hystrix possesses spines anterior to the main tract of long spines and guard-hairs, i.e. on the anterior flanks and shoulders? This unusually revealing photo seems to show that, when the pelage is fully activated by pilo-erection, this includes short dark spines interspersed among the short dark hairs on these parts of the body. If so, I have never seen this mentioned in the literature.

Posted by milewski about 2 months ago (Flag)

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