Velvet Worms: these cute little creatures are actually voracious predators that capture their prey with a projectile slime known as the "silly string of death"
Onychophorans, also known as velvet worms, look almost like a cross between a caterpillar, a millipede, and a worm, but they actually belong to their own unique phylum.
Above: a velvet worm of the genus Eoperipatus
The velvet worm's fleshy antennae, chubby little feet, and gleeful expression might make it seem kind of cute, at least at first glance, but these creatures are ferocious predators that prey on terrestrial arthropods like crickets, cockroaches, and spiders. In order to immobilize their prey, they shower their victim with a remarkably strong and quick-drying adhesive.
Above: another Eoperipatus species
As this article explains:
The velvet worm, a squishy little predator that looks like the stretch-limo version of a caterpillar, has a whimsical MO: it administers death by Silly String.
In the leaf litter of tropical and temperate forests around the world, velvet worms stalk the night on dozens of stubby legs. The pocket-size predator—whose species range from less than half an inch to eight inches long—can barely see, so it bumbles around, hoping to literally bump into an edible bug such as a cricket or a woodlouse. When it finds one, the velvet worm uses nozzles on either side of its face to shoot jets of sticky slime at its victim.
Above: genus Peripatoides and genus Eoperipatus
Velvet worm slime is ejected as a liquid, but it rapidly hardens into a gel as it soars through the air, forming fibers that are as strong as nylon. The substance then solidifies into glassy adhesive fibers as soon as it hits the target, trapping the victim in an inescapable net.
The slime can hit its target from up to 1.5 feet away.
Above: close-up of a velvet worm spraying its slime
The slow-moving velvet worm then approaches its prey, pierces the victim's exoskeleton with a pair of blade-like jaws, uses its saliva to dissolve the insect's innards, and then quickly devours its meal.
Above: the velvet worm's horrifying face as it prepares to feed
Velvet worm slime is quick-setting, strong, dissolves in water, and can also be reconstituted into new fibers. The mechanisms that produce these properties were unknown until just 16 years ago, when an Australian scientist discovered that the slime contains "chaotic proteins:"
The proteins are loaded with amino acids that repel one another, and they’re short of the water-repelling ones that help other proteins to establish a solid core. Rather than folding, they adopt open and random structures that are extensively coated with water molecules. Their watery sheaths prevent the protein molecules from interacting with one another. They can only do so when the water disappears. And that’s exactly what happens when the slime hits its target.
Insects are covered in waxy, water-repellent shells, but the velvet worm’s slime contains fat and detergent molecules that break past this defence. These chemicals, and the sheer force with which the slime is shot, means that it spreads all over the victim. The insect’s struggles seal its fate by drawing the slime into threads. Spread over a large surface area, the water in the slime quickly evaporates, unsheathing the proteins and leaving them to mingle for the first time. They form tight chemical bonds with one another and the once-liquid slime hardens.
Above: Eoperipatus feeding on an unknown arthropod and Peripatoides suteri feeding on a huntsman spider
Velvet worms are some of the oldest terrestrial animals on Earth, dating back to nearly 540 million years ago, when most of the world's creatures were still confined to the oceans. They're older than dinosaurs, trees, sharks, and even horseshoe crabs.
Surprisingly, their morphology has changed very little in the last 400 million years or so -- their fossilized ancestors look remarkably similar to the velvet worms that are still roaming the earth today.
Above: assorted velvet worms
The world's smallest species of velvet worm is Ooperipatellus nanus, with a length of just 5mm (0.2 inches); the largest is Mongeperipatus solorzanoi, which can grow to a length of 22cm (8.7 inches). Velvet worms can have between 13 and 43 pairs of feet, depending on the species
Above: the tiny feet of a velvet worm
The term Onychophora literally means "claw-bearer," which is a reference to the hooked claw at the tip of each foot. Together, these claws allow the worm to travel across uneven terrain, but they can also retract as it moves onto smoother surfaces. When the claws are retracted, the worm simply walks on the stubby little pads of its feet.
Above: Epiperipatus barbadensis
Phys.org: Velvet Worm Slime
National Mag Lab: Cracking the Chemical Code of the "Silly String of Death"
National Geographic: Scientists Uncover Secret of the Velvet Worm's Quick-Setting Slime
Scientific American: Velvet Worm Slime Reveals its Sticky Secrets
Journal of the American Chemical Society: Peculiar Phosphonate Modifications of Velvet Worm Slime Revealed
Onychophoran Website: Onychophora
ZooKeys: An Updated World Checklist of Velvet Worms
iNaturalist: Velvet Worms
Harvard Magazine: Creepy Crawlies and Sticky Murder Weapons at Harvard
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