Velvet worms (Onychophora) are ancient, soft-bodied invertebrates that have roamed terrestrial environments for over 500 million years. Despite their slow, caterpillar-like movement, they are lethal ambush predators capable of capturing nimble prey like crickets, spiders, and termites. Their secret weapon is a pair of oral papillae—specialized glands on their heads—that squirt high-speed jets of proteinaceous slime up to several centimeters away.
What makes this liquid projectile system a masterpiece of biomechanics is how the slime is generated and how it rapidly transitions from liquid to solid. Inside the worm's body, the slime is stored as a high-density, water-based solution of lipid-protein complexes. Rather than using muscle contraction to aim, the velvet worm utilizes fluid dynamics: liquid flows through narrow papillae channels, causing natural oscillating instabilities that swing the nozzles back and forth up to 30 times per second, spraying a crisscrossing web without burning extra energy.
Upon contact with the target or surrounding air, shear stress and water evaporation trigger a rapid physical transformation. The hydrophobic (water-repelling) lipid components within the slime assemble into dense, insoluble fibers, trapping water molecules and instantly cross-linking proteins. The resulting network stiffens within seconds into a tough, sticky glue that binds tightest when the prey struggles.
Because the slime is hydrophobic once set, environmental humidity or rain cannot dissolve the trap. After paralyzing its catch, the velvet worm approaches, injects digestive enzymes, and eats both the prey and its spent slime, recycling the precious protein investments.