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Porcupines

The quills are barely attached to the porcupine and grip hard onto whatever they enter. Nothing needs to be thrown.

No porcupine can throw a quill. The quills are barely attached to the porcupine and, in American species, carry backward-facing barbs that make them easy to drive in and hard to pull out — so touching one transfers them, without anything being fired.

The shooting myth is old, persistent, and has a mechanical explanation better than the myth. A porcupine quill is a modified hair, and it is held in the porcupine’s skin loosely — deliberately so. When an attacker makes contact, the quill goes in, and because it is held far more strongly by the tissue it has entered than by the porcupine, it detaches. Nothing was propelled. The animal simply arranged for the quill to prefer the attacker. What makes the attachment asymmetric is microstructure, and it was measured directly. North American porcupine quills carry microscopic backward-facing barbs near the tip. Driving the quill in, those barbs concentrate stress at their tips and actually *reduce* the force needed to penetrate tissue — a barbed quill goes in more easily than a smooth one. Pulling it out, the same barbs catch, and withdrawal force rises substantially. Two opposed requirements, optimised independently by one structure. Old World porcupines mostly lack barbs and rely on a different approach: they are larger, their quills are longer and thicker, and they reverse into an attacker rather than depending on a chance touch. That two unrelated families arrived at quills at all is a convergence worth noting, and their differences are a reminder that "porcupine" names a body plan rather than a lineage. Where the impression of throwing comes from is not mysterious. A defending porcupine shakes and rattles its quills, and loose ones — already detached or nearly so — can come free and travel a short distance. Somebody standing close, being rattled at, who then finds a quill in their leg, has all the evidence they need for a conclusion that happens to be wrong.

Early coverage · 37% complete · reviewed 2026-09-03

What this page covers

Two unrelated families that arrived at quills independently: Old World porcupines in Africa and Asia, and New World porcupines in the Americas. Their quills differ, and only the New World species have barbed tips.

Often confused with: Hedgehogs and echidnas, which have spines and are not related to porcupines or to each other; A single group, when Old World and New World porcupines are separate families; Animals that shoot quills, which none of them can do

Quick facts

Quills are not projectile
No porcupine has any mechanism for throwing one
What the barbs do
Reduce the force to enter, and increase the force to remove
Two separate families
Old World and New World porcupines evolved quills independently
Where the myth comes from
Loose quills shaken free during a rattling defensive display

Why nothing needs to be thrown

The quill is held loosely by the porcupine and tightly by whatever it enters.

No porcupine can throw or shoot a quill. The quills are loosely attached to the porcupine and, thanks to backward-facing barbs, strongly attached to whatever they enter — so contact alone transfers them.

Established

Specialists would state this without hedging. Multiple independent lines of evidence agree.

Porcupine quills are not projectile. In North American porcupines, microscopic backward-facing barbs reduce the force required for tissue penetration while substantially increasing withdrawal force. Combined with weak attachment to the porcupine’s skin, this results in quill transfer on contact without any propulsive mechanism.

Who this applies to
Barb mechanics measured in the North American porcupine; the absence of any throwing mechanism applies to all porcupines.
Studied in
Erethizon dorsatum, Hystricidae
Why we rate it this way, and what the caveats are
EstablishedHigh confidence

The mechanics were measured directly, and the absence of a projection mechanism is a straightforward anatomical fact.

How far it can be extended

No porcupine possesses musculature capable of projecting quills; barb structure varies, with many Old World species lacking barbs.

Caveats

  • Loose quills can be dislodged by a shaking porcupine and may travel a short distance, which is probably where the impression of throwing comes from.
  • Old World porcupines have differently structured quills, many without barbs, and rely more on backing into an attacker.

Still unanswered

  • How quill barb geometry varies across porcupine species and whether it tracks their principal predators.

Last reviewed 2026-09-03

The evidence (1 study)

How we know

Measuring what a quill barb actually does

Porcupine quills carry microscopic barbs. Do they make the quill harder to remove, harder to insert, or both?

The force required to drive quills into tissue and to withdraw them was measured, comparing natural barbed quills against quills whose barbs had been removed, and against synthetic replicas with and without barb structures.

What happened

Barbs reduced the force needed for penetration — by concentrating stress at the barb tips — while substantially increasing the force needed for withdrawal. Barbed quills entered more easily and resisted removal far more strongly than debarbed ones.

What it shows

One structure independently optimising two opposed requirements. It also explains the shooting myth mechanically: a quill held loosely by the porcupine and gripping hard in whatever it enters will transfer on contact, with nothing propelled.

What it does not show

Forces were measured in tissue analogues and animal tissue rather than during a live predator encounter. The measurements are from North American porcupines, and Old World species mostly lack barbs entirely, so this is not a general account of porcupine quills.

The controls — what makes this evidence rather than a story
  • Debarbed natural quills as the comparison, so the variable is the barb rather than the quill.
  • Synthetic replicas, which separate the effect of the geometry from any other property of porcupine keratin.
  • Penetration and withdrawal measured separately, since the interesting result is that they go in opposite directions.

From Microstructured barbs on the North American porcupine quill enable easy tissue penetration and difficult removal

The barb result is the genuinely surprising part, and it is counter-intuitive in a useful way. You would expect barbs to make penetration harder, since they are irregularities dragging through tissue. They do the opposite: by concentrating force at a series of small tips rather than distributing it along a smooth taper, they lower the force needed to enter. The same geometry then catches on withdrawal. One structure, two opposite requirements, both improved.

Diagram

One structure, two opposite requirements

Held loosely by the porcupine, hard by whatever it enters.

One structure, two opposite requirementsGoing inbarbs concentrate force — less push neededComing outthe same barbs catch — much more pull neededHeld loosely by the porcupine, hard by whatever it enters. Nothing is thrown.
The same explanation in words

A quill shown twice. Going in: backward-facing barbs near the tip concentrate force at a series of small points rather than spreading it along a smooth taper, so less push is needed to penetrate tissue — an arrow marks the direction of entry. Coming out: the same barbs catch against the tissue, and a much larger pulling force is required. Because the quill is weakly anchored in the porcupine’s own skin and strongly anchored in whatever it enters, contact alone transfers it. Nothing is thrown or propelled.

Two families that arrived at quills separately

Old World and New World porcupines are not close relatives.

The two groups are rodents and that is roughly where the relationship ends. Old World porcupines occur across Africa, southern Europe and Asia; New World porcupines are American, and several are competent climbers, which is not what most people picture. They acquired quills independently, and the quills differ accordingly: Old World species have longer, thicker, mostly unbarbed quills, while the New World species carry the barbed microstructure that has been measured.

Hedgehogs and echidnas are neither, and are not related to porcupines or to each other. Four separate arrivals at the same idea — modified hairs stiffened into spines — is a reasonable indication that it is a good idea for a slow animal that cannot run.

The wider pattern

  • Armour and spines

    Why protection concentrates in animals that were never going to outrun anything

The defence runs in order

Warning first. Quills are the last step, because losing them is costly.

  1. Display. The animal raises its quills, which makes it look considerably larger and advertises what it is.
  2. Sound. Quill rattling and teeth clattering, which is a warning rather than an attack.
  3. Smell. A pungent odour from skin glands, another signal that this is a porcupine and not worth it.
  4. Orientation. It turns its back and reverses towards the threat, presenting the quills rather than the face.
  5. Contact. Only now do quills transfer — and each one lost has to be regrown.

That sequence is worth reading as a cost structure. Every earlier step is cheap and reversible; the last one costs the animal quills and risks injury. It follows the same pattern as chemical defence, where the warning exists precisely so the expensive part is not needed — and it is why a porcupine that has been given room will usually take it.

Related

Claims about this, checked

Things people have heard, and what the evidence actually supports.

The research behind this page

1 studies, newest first. Each one has a page explaining what it found and what it could not show.

2012Proceedings of the National Academy of Sciences

Microstructured barbs on the North American porcupine quill enable easy tissue penetration and difficult removal

The backward-facing barbs reduce the force needed to penetrate tissue — by concentrating stress at the barb tips — while substantially increasing the force needed to withdraw the quill.

Where to go from here

Each of these follows from something on this page — a relationship in the evidence, a claim people ask about, or the next mechanism along.

How complete this page is, and what it is still missing

NatureHQ publishes its own gaps. This page is at 37% completeness against what we would call a finished subject, and was last reviewed on 2026-09-03. It carries 1 claims and answers 8 mapped search questions.

  • no research from the last few years is attached — check for newer work
  • more experiments could be explained in plain English
  • Diet, reproduction and ecology are outside this page, which is about the defence.
  • Barb structure has been measured in North American porcupines; how it varies across species is not established.
  • Old World porcupine defence is described in outline and is less well studied.