Similarities/differences between the porcupines of different Hemispheres: Erethizon vs Hystrix, part 4


continued from


Hystrix is one of the few genera of plant-eating mammals on Earth that qualify as possibly possessing warning colouration at the scale of the whole body. Another, Lophiomys (, is toxic instead of spiny. In none of these genera is the overall pattern stark enough to qualify as warning colouration without the pelage being activated.

Erethizon qualifies for warning colouration only tenuously, because the pattern

  • is only conspicuous once activated,
  • is restricted to a smaller proportion of the body than in Hystrix, and
  • is poorly-developed in certain individuals/regions/seasons.

The tail differs between Erethizon and Hystrix in various ways.

In Erethizon, the tail is large and used in posture and locomotion. On this basis it is unsurprising that it is also particularly important in anti-predator warning (conspicuous colouration, plus the sound of slapping) and defence (retaliatory striking to deploy caudal spines).

In Hystrix, the tail seems to play a negligible role in posture or locomotion. It may play an important role in deploying spines in H. brachyura and H. javanica.

However, in the other three species of Hystrix, the tail

Overall, Erethizon emerges as the lineage with the greater emphasis on the adaptive value of the tail.

If we disregard the tail, 'porcupines' can perhaps be compared in various ways with the koala, sloths, and mole-rats.

Erethizon somewhat resembles the koala ( in being able to survive on nutrient-poor, toxic leaves for months at a time (see and However, the analogy is limited because Erethizon

  • does so only after laying down large deposits of fat in autumn, and
  • eats bark and cambium in winter, as an extremely fibrous nutrient-supplement.

Alternatively, Erethizon somewhat resembles sloths (, all the North American species of which were larger-bodied and have recently become extinct.

Erethizon differs from both the koala and sloths in the development of its incisors ( and

Hystrix instead somewhat resembles mole-rats, despite the differences in body size.

Across its distribution in Africa and Eurasia, Hystrix coexists with many genera and species of mole-rats belonging to three families ( The North American counterparts are gophers (Geomyidae,

Portrayal of Erethizon as an undersize ground-sloth and Hystrix as an oversize gopher is

  • admittedly just caricature, and
  • counter to the observation that it is Erethizon that, in most ways, looks more like a gopher.

However, this portrayal conveys some of the actual adaptive differences between these versions of 'porcupine'.

Approaching this discussion from a different perspective:

If a given species possesses extreme armour/weaponry, is this in addition to normal anti-predator adaptations, or instead of them?

To the degree that tortoises are typical of armoured animals, their slow-movement suggests that the answer may usually be 'instead of'.

How do Erethizon and Hystrix fit into this conceptual framework?

Erethizon seems below-par in the following normal adaptations:

This suggests that Erethizon relies largely on its spines - and the associated syndrome of warnings (including odour), body-orientation, and tail-wielding - for protection from predators. Such specialisation is noteworthy given that the unexcited animal looks fairly defenceless until it spreads the pelage around the particularly spiny rump.

In the case of Hystrix, the only adaptations that seem below-par are eyesight and braininess. The armour/weaponry is obvious even when the animal is unexcited, but the animals retain locomotory speed and, in their capacity to bear up to four offspring per year, considerable fecundity.

In explanation of this, there are differences in the predatory regimes (excluding Homo sapiens,

Erethizon is vulnerable mainly to Pekania pennanti ( and and Puma concolor (

By contrast, three of the species of Hystrix are vulnerable to a guild consisting of several coexisting species:

Inasmuch as the predatory regime is particularly intense and diverse in the case of the African species, this may help to explain why Hystrix has retained relatively rapid locomotion and reproduction, in addition to its extreme armour/weaponry.

Several remarkable videos show Hystrix africaeaustralis defending itself against Panthera pardus. (Note that both the felid and the rodent possess whitish caudal flags.) and and and and and and and and and and and and and and and and and and

The above include enough evidence from Kruger National Park, in particular, to suggest that nimble manoeuverability is essential to the anti-predator reactions of Hystrix.

Panthera pardus seems to find it relatively easy to kill H. africaeaustralis in culverts (cylindrical drains, made of concrete or metal, for stormwater, running under the road from one side to the other, and

By contrast, when the encounter takes place on the surface of the road, the rodent seems relatively secure as long as it does not move off the open space.

I infer that H. africaeaustralis prefers the exposure of the road because it can keep orienting its body without obstruction. When in the culvert it is relatively constrained. It can fill the tunnel with the erect pelage while keeping its back to the predator. However, the felid can presumably snag the hindfeet by reaching forward at ground-level, thus knocking the rodent off its feet, in a way that would be impossible were the refuge a relatively narrow, natural burrow.

Posted by milewski milewski, May 08, 2022 03:02


The apparently greater osteophagy by Hystrix than by Erethizon suggests that the extreme pelage of the former places particular demands on calcium. Pelage, including even the largest spines, is composed of a plastic-like protein, keratin. However, are the spines - which are frequently shed and replaced in Hystrix regardless of their actual deployment in defence - fortified with calcium?

Posted by milewski about 2 months ago (Flag)

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