An elephant's tusk and a snail's "love dart" have almost nothing in common — except that both are built to pierce something. A new study finds that across 143 of nature's puncture tools, evolution keeps running into the same basic trade-off, no matter what animal is doing the stabbing.
Researchers led by Philip Anderson at the University of Illinois Urbana-Champaign measured the shape of an eclectic set of biological piercing implements: tusks, shark teeth, porcupine quills, cactus spines, fangs, stingers, claws, beaks, the needlelike ovipositors parasitic wasps use to lay eggs inside other insects, and — perhaps the strangest entry — the calcified "love darts" that hermaphroditic land snails fire into their mates during courtship, as well as the piercing organs male bedbugs use during mating. The findings were published in the journal Science Advances, according to Science News.
The team scored each tool on two properties: taper, or how long and slender it is, and roundness, meaning whether its cross-section is closer to a circle or flattened like a blade. Tools that are highly tapered and flatter turn out to pierce material more easily but snap more readily under stress. Stubbier, rounder tools resist breaking but require more force to punch through in the first place.
No single shape won out. Instead of clustering around one "ideal" piercer, the 143 tools spread out along that trade-off, each representing a different balance between piercing efficiency and durability — a spike optimized for one property generally gives up some of the other.
Shape didn't reliably track function, either. Love darts, despite being used for one purpose only — jabbing snail flesh — varied wildly in form across species. Tools used for injecting venom or fluid, however, did tend to be rounder, likely because a hollow center for delivering liquid requires a less blade-like cross-section.
You don't need horror movies if you study puncture biology.
Philip Anderson, University of Illinois Urbana-Champaign
The research adds to a growing body of work treating puncture as its own mechanical problem, one that recurs so often across the animal and plant kingdoms — and evolved so many separate times — that engineers have started mining it for ideas on everything from surgical needles to microneedle drug patches.