Velvet worms, caterpillar-like invertebrates with long antennae and cartoonish faces, are strange enough on their own. "Their whole body is built of concentric rings, a bit like the Michelin Man," says Richard Fortey, author of the book Horseshoe Crabs and Velvet Worms.
But these creatures, which have been on Earth for a long, long time, are also unusual in their ability to shoot jets of slime at their prey.
Each worm has a pair of slime glands, located below their antennae, that squirt a sticky mucus. The milky-white goo covers the victim in a net of slime, immobilizing it for easier eating.
Though scientists have studied velvet worms for over a century, they didn't know the mechanism underlying the critters' superfast squirts.
That's because the velvet worm's jet swings rapidly, which is rare in nature.
Most animals that squirt or spit, such as archerfish, do so in a straight line. Animals that produce oscillating jets of fluid, such as spitting cobras and spitting spiders, produce their spray by moving their heads. (See "Mystery Solved: How Archerfish Shoot Water at Prey With Stunning Precision.")
However, the velvet worm's head remains in a fixed position as it squirts, leaving scientists perplexed.
Watch a video of the slime "cannon attack."
That is, until now. An international team of researchers recently used a combination of high-speed video and anatomical analysis to discover that the animals use elastic glands and fluid forces instead of muscle power to shoot slime.
In recent experiments, Andrés Concha, of Adolfo Ibañez University in Santiago, Chile, and colleagues studied a species of giant velvet worm (Peripatus solorzanoi) that is nearly 10 inches (25 centimeters) long.
Though some velvet worms are smaller than an inch long, Concha and colleagues chose to study the larger species to better visualize its slime spitting.
First, the researchers filmed several velvet worm attacks using high-speed video. They ruled out the possibility that the rapid squirting was the result of muscular contractions, because the slime jet's swinging speed was faster than the worm's muscle movements. (Also see a video of a blood-squirting lizard.)
Next, Concha and his colleagues examined the velvet worm's anatomy under a microscope. The team found the slime glands—called oral papillae—are soft tubes that can fold and unfold quickly like an accordion, according to the study, published March 17 in the journal Nature Communications.
Connected to the oral papillae is a reservoir system where slime is stored. The reservoir contracts and drives the slime through a small duct in the papilla, a syringe-like action that accelerates the slime's movement.
The papillae then work like a garden hose—as the slime travels through them, the glands' soft, elastic nozzle waves around, causing the goo to form a net of slime.
"Our analyses show that muscles are not needed," says Concha.
Fortey, also a paleontologist at London's Museum of Natural History, says the study shows "'primitive' animals can evolve sophisticated techniques of attack and defense using apparently simple materials."
Concha adds there is still more to learn about this simple slime, such as its molecular makeup. But one thing he knows from experience is that it's "a very good glue."
"One of the worms managed to squirt directly onto our camera," he says, "and two years later, the slime is still stuck there."