It may be smaller than a grain of rice, but the aptly-named porcupine-Velcro millipede Polyxenus fasciculatus is one tough cookie.
When assaulted, often by an ant or spider, it turns tail but doesn't run. Its rear end is equipped with two tufts of microscopic bristles, each shaped like a grappling hook. As the millipede pivots, it splays these weapons and swipes them against its assailant. Many of the bristles snag on the hair-like setae on the insect's face and front legs, and are pulled free of the millipede as it flees.
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These weapons then do the rest. The shaft of each bristle is covered in hook-like barbs that further entangle the attacker as it tries to brush them off.
The loose bristles interlock in a similar fashion to Velcro, acting like a self-assembling net. After a few moments of struggle, the aggressor finds itself hog-tied and left to die.
The millipede never runs out of ammo. It has enough bristles for multiple attacks, and its full arsenal is renewed at every moult - in fact, using them may spark moulting.
The tactic almost never fails in this North American species.
But closely related millipedes in Brazil and Central America that use this same defence have met their match.
Thaumatomyrmex ants have evolved long, smooth, pitchfork-like mandibles, which they use to trap and hold their prey at a distance. The captive's tufts, too short to touch the ant's face, are rendered useless. The predator then kills with a sting of venom, carefully strips its 'coat of arms' and enjoys the meal. David