The velvet worm (phylum Onychophora) is an ancient terrestrial invertebrate that has remained largely unchanged for millions of years. Often described as a caterpillar with legs, this soft-bodied animal has numerous pairs of short, stumpy appendages, giving it a distinctive velvety texture. They are exclusively found in humid environments, primarily inhabiting tropical and temperate forests across the Southern Hemisphere. Here, they lead a secretive, predatory life among leaf litter and decaying wood. This phylum represents an evolutionary link between segmented worms and arthropods, known for a unique hunting method.
Primary Food Sources
Velvet worms are active carnivores that prey on a variety of smaller invertebrates found within their damp, detritus-rich habitat. Their diet consists mainly of soft-bodied or relatively small arthropods that they can successfully subdue and consume. Specific targets include:
- Woodlice
- Termites
- Small spiders
- Snails
- Various insect larvae like grubs and caterpillars
The size of the prey an individual velvet worm can hunt is limited by its own body size, which can range from a few millimeters up to 22 centimeters in the largest species. They are nocturnal hunters, slowly navigating the dark forest floor using chemical and touch sensory input to locate their next meal. The availability of these small creatures is highest in the moist microclimates where the velvet worm must live to prevent desiccation.
Their role in the ecosystem is that of a specialized predator, helping to regulate populations of small ground-dwelling organisms. This predation places them at a higher trophic level, making them a significant component of the forest floor food web. They are particularly efficient at capturing prey that is not heavily armored or too fast to escape their immobilization technique.
The Unique Hunting Strategy
The velvet worm’s method of capturing prey involves a rapid-fire adhesive jet. When a potential meal is detected, often through sensitive antennae, the worm stalks the invertebrate until it is within range. The worm then uses a pair of modified appendages near its mouth, called oral papillae, to shoot a stream of quick-hardening, milky-white slime.
This proteinaceous fluid is ejected at high speed, with some species capable of accurately hitting a target up to 30 centimeters away. The slime is expelled in a rapidly oscillating stream, which is not caused by muscle movement but by a passive physical phenomenon. This rapid oscillation, occurring at frequencies between 30 and 60 Hertz, causes the jet to spray out in a wide, disorganized web that instantly entangles the prey.
Upon contact with the air, the slime quickly changes from a liquid to a solid state, trapping the insect or spider in a sticky, fibrous net. The immobilized prey is cemented to the ground, preventing escape, and the slime is also used as a form of self-defense against potential threats.
Consumption and External Digestion
Once the prey is securely immobilized in the slime, the velvet worm slowly approaches its captive. The worm uses its antennae to explore the trapped animal, searching for a weak spot in its exoskeleton or skin. It then uses a pair of sharp, crescent-shaped mandibles, or jaws, located within its oral cavity, to puncture the prey’s body.
After piercing the outer layer, the velvet worm injects a digestive saliva containing potent enzymes into the captured invertebrate’s body. This process is a form of external digestion, where the internal tissues of the prey are chemically broken down and liquefied outside of the worm’s own body.
The worm waits for the enzymes to complete their task, a process that depends on the size of the meal. The velvet worm then sucks up the resulting liquefied tissue through its pharynx, consuming the meal. The worm will often consume the dried, protein-rich slime along with the meal, recycling the material used for the capture.