Cactus Spines Serve Several Purposes Besides Poking Hikers

By Casey Kuhn
Published: Thursday, February 7, 2019 - 5:42pm
Updated: Friday, February 8, 2019 - 12:41pm

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cholla cactus spine
Stephanie Crofts
This scanning electron micrograph shows a close up of a jumping cholla spine. Note the barbed tiles that allow for easy puncturing, but difficult removal.

Cacti have evolved spines to keep away animals who want to eat them, and to help reproduce. 

Researchers like Stephanie Crofts at University of Illinois stuck cholla cactus spines into a half pound chunk of pork shoulder to see what would happen.

“A single spine embedded like, maybe 2 millimeters at most, would lift up the entire chunk of meat and it was, like, mindblowing!”

The lab Crofts works in specializes in the physics of natural punctures, like porcupine quills and snake fangs.

As many an unsuspecting Arizona hiker has experienced, jumping chollas are notorious for their stickiness.

That’s because the spine is shaped with miniature barbed tiles, making it easy to puncture but hard to remove.

Crofts says that special shape helps the cactus to spread and reproduce.

That’s in contrast to a golden barrel cactus, whose spines are smoother.

“They don’t really seem to be using this reproductive strategy, they depend more on the tried and true flowers and pollinators," Crofts said. "That’s why you don’t really see chunks of saguaro and barrel cactus falling off and starting new plants.”

Ultimately, those spiny shapes determine whether the cactus needs them for reproduction, like the cholla, or defense, like the barrel.

The cholla spine has evolved in a remarkably similar way to porcupine quills, which Philip Anderson, who runs the puncture-studying lab, has also studied.

“Lots of different organisms do it, and they do it with different scales and different materials, but they all have to follow the same basic rules of how you puncture something," Anderson said. "So it’s kind of a really useful case study for looking at this broader question in evolution.”

Ultimately, the spine shapes at a micro level determine how they poke animals — and hikers — and the research can be used for things like needle and defense development.

Cholla cactus meat experiment
L. Brian Stauffer/University of Illinois
A half-pound of pork shoulder is suspended from one jumping cholla spine.
Stephanie Crofts and Philip Anderson
L. Brian Stauffer/University of Illinois
Stephanie Crofts and Philip Anderson study puncture mechanics at the University of Illinois.

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