Velvet worms, ancient invertebrates that have roamed Earth’s humid forests for over 500 million years, are intriguing creatures. These soft-bodied animals, known as Onychophora, stand apart from arthropods and tardigrades. They have captured scientific attention for a remarkable biological material they produce: a specialized slime. This adhesive substance, deployed with surprising precision, holds unusual properties and offers potential insights for various scientific and engineering fields.
The Unique Properties and Mechanism of Velvet Worm Slime
Velvet worm slime is a complex biological material, primarily composed of large protein molecules, fatty acids, and water. These components combine to form tiny, uniform nanoglobules, each about 75 nanometers in diameter. Researchers have also identified encapsulated phosphate and carbonate salts within the slime. The arrangement and interaction of these constituents give the slime its unusual physical properties.
The slime exhibits a rapid transition from a liquid to a solid, sticky gel upon expulsion. This transformation is not simply due to air exposure but is significantly influenced by mechanical forces, such as the struggles of captured prey. As the slime is ejected, shear forces cause the protein nanoglobules to rupture and self-assemble into stiff, strong filaments. These filaments are composed of long protein fibers encased by a layer of lipids and water molecules.
The velvet worm deploys its slime through two oral papillae, elastic tubes on either side of its head. Muscles surrounding the slime reservoir contract, forcing the fluid through a funnel-shaped duct, increasing its velocity. The oral papillae then oscillate at approximately 30 Hz, producing two slime jets that form a wide, sticky fiber mesh. This spraying mechanism allows the worm to cover a significant area, sometimes up to 10-30 centimeters, in milliseconds.
The hardened slime is recyclable. Unlike many synthetic adhesives, the solidified slime can be re-dissolved in water, returning to its original liquid state. This reversibility is linked to the protein structures within the slime, which can re-form from the dissolved nanoparticles. The slime also contains phosphonate groups, a chemical modification where phosphorus bonds directly to a carbon atom, believed important for fiber formation.
Predation and Defense: The Slime’s Purpose
The primary function of velvet worm slime is for predation. These nocturnal, slow-moving predators rely on their slime-shooting ability to capture prey. When a velvet worm detects a small invertebrate, such as an insect or spider, it rapidly ejects sticky slime. This adhesive jet quickly immobilizes the target, ensnaring it in a web-like network of fibers.
The slime’s ability to harden upon mechanical stimulation, like the struggles of prey, makes it effective. This ensures that the more the prey attempts to escape, the stronger and more entangled the trap becomes. Once immobilized, the velvet worm can approach and consume its internal fluids using its sharp jaws. This hunting mechanism is a defining characteristic of the phylum Onychophora.
Beyond hunting, the slime also serves as a defensive mechanism against predators. When threatened, velvet worms can spray their slime to deter attackers or create a physical barrier. This sudden, sticky spray can startle or entangle potential threats, allowing the worm to escape. The slime’s deterrent effect helps the worm avoid engagement with predators.
Biomimicry and Potential Applications
The properties of velvet worm slime have made it a subject for biomimicry, inspiring scientists and engineers to explore its potential for new materials. Researchers are interested in replicating its rapid liquid-to-solid transition and its water-soluble, recyclable nature. The slime’s ability to dissolve and re-form offers a blueprint for sustainable material design, unlike most synthetic polymers which are difficult to recycle.
One area of application lies in the development of new adhesives. The slime’s non-toxic, biodegradable composition makes it a model for creating environmentally friendly glues. Its ability to set quickly and strongly, even in moist environments, could lead to advancements in surgical glues for medical procedures. Such bio-inspired adhesives could offer more targeted and safer alternatives for closing wounds or attaching tissues.
The hardening mechanism of the slime, particularly its response to mechanical forces, is also being studied for potential use in robotics. Scientists are developing “smart” materials that can change stiffness rapidly, mimicking the slime’s behavior. For instance, a velvet worm-inspired adhesive robotic system has been proposed, utilizing structured magnetorheological materials that can precisely control adhesion through rapid stiffness changes. This could enable delicate grasping of soft or wrinkled surfaces.
Insights from velvet worm slime could contribute to more sustainable pest control methods, where biodegradable, non-toxic traps could be developed. Understanding the slime’s molecular structure and phase transition mechanisms, especially the role of phosphonates, is a step towards creating next-generation recyclable bioplastics and other advanced materials. Researchers aim to develop materials that are both strong and easily recyclable.