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This unassuming worm hunts with a self-assembling slime net. Here\u2019s what scientists have uncovered about its biology, behavior and evolution.<\/p>\n
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When picturing a predator, most people envision an animal with immense speed, sharp teeth or deadly venom<\/a>. But velvet worms (Onychophora) are perhaps the opposite. They\u2019re slow and soft-bodied, and yet they\u2019re also remarkably effective hunters. This is thanks to a built-in weapon that you wouldn\u2019t believe until you saw it for yourself: a slime cannon that fires liquid threads into the air to create woven, gooey traps.<\/p>\n After decades of careful experimental work, researchers have fully unpacked the different factors that make this strategy so effective, from biomechanics to materials science. Here\u2019s how it works, what the slime is made of and why evolution arrived at something so unusual in the first place.<\/p>\n How The Velvet Worm Produces Slime<\/p>\n The velvet worm\u2019s slime begins as a liquid stored inside specialized glands that run along the animal\u2019s body. When needed, the liquid is expelled through a pair of small structures near the head (oral papillae) in two rapid jets. <\/p>\n In a 2017 study<\/a> published in Nature Communications, researchers analyzed the makeup of this viscous fluid and discovered that it\u2019s a highly structured protein solution. Inside the worm, it exists as a suspension of microscopic particles known as nanoglobules, which are composed primarily of proteins and lipids. These nanoglobules act as building blocks, and they\u2019re held in a stable, liquid state.<\/p>\n But as soon as it\u2019s ejected, something remarkable happens. As the slime stretches through the air and encounters mechanical stress, those nanoglobules begin to reorganize. The proteins rapidly assemble into solidifying fibers, which transform the fluid into a network of sticky threads. <\/p>\n What\u2019s especially remarkable is that this process doesn\u2019t rely on any heat, chemical curing or external catalysts. It\u2019s driven primarily by mechanical forces and changes in the physical environment, such as shear stress and water evaporation. This means that the slime is essentially preloaded with everything it needs to become a fiber. The act of firing it does the rest.<\/p>\n The elegance of this system lies in the stored potential that the worm releases under the right conditions; the worm doesn\u2019t \u201cbuild\u201d fibers itself in the traditional sense. The result is a material that transforms from a liquid to a solid in fractions of a second, to form adhesive strands that are both elastic and strong.<\/p>\n What\u2019s perhaps most intriguing, as confirmed in a 2019 study<\/a> from Integrative and Comparative Biology, is that this process is, to some extent, reversible. The authors explain that fibers from the extracted slime can be dissolved in water, and new fibers can be drawn from the resulting solution. This indicates that the process is likely encoded in the slime\u2019s biomolecules.<\/p>\n When The Worm\u2019s Cannon Fires<\/p>\n Velvet worms are nocturnal hunters that move through leaf litter, rotting logs and other cluttered, low-light environments. Because their bodies lack the speed and rigidity necessary to chase down prey, they have to rely instead on proximity and precision<\/a>.<\/p>\n According to a 2015 study<\/a> published in Integrative and Comparative Biology, the velvet worm\u2019s slime cannon is deployed in two primary contexts: when capturing prey or deterring predators.<\/p>\n When hunting, the worm approaches slowly, often within a few centimeters of its target, which are typically small arthropods like insects. Then, in a rapid burst, it fires two streams of slime that oscillate as they travel. This oscillation causes the streams to cross and spread, which forms an adhesive net-like structure in mid-air.<\/p>\n The effect is immediate. The prey is entangled in a mesh of sticky threads that leave their legs, antennae and body segments bound together. And the more they try to wriggle their way out, the tighter and more adhesive the fibers become. Within moments, the prey is effectively immobilized. The worm can then approach safely and deliver its digestive enzymes through its jaws, beginning the process of external digestion.<\/p>\n Against predators, they leverage the same mechanism as a defensive tool. A well-aimed spray can coat the mouthparts or limbs of an attacker, which impairs its ability to grasp or bite. The slime doesn\u2019t need to injure or envenom the prey; it only needs to discombobulate the predator. For such a slow-moving worm, a brief delay can make the difference between escape and capture.<\/p>\n What stands out here is the dual use of the system. Many biological weapons are specialized: venom is used for predation, armor is used for defense, and so on. But the velvet worm\u2019s slime serves both roles, without any modifications needed. It is a general-purpose solution to a set of recurring problems: how to subdue something faster than you, and how to avoid being subdued yourself.<\/p>\n Why Evolution Produced A Worm With A Slime Cannon<\/p>\n