Velvet worms are bizarre creatures living in leaf litter on the floors of tropical forests. They superficially resemble caterpillars and are called "worms with legs," but they're their own phylum, Onychophora, which means "claw-bearers." This is a reference to the small chitin claws on their stub feet. Growing to between 0.5 and 50 cm (0.2 - 12.5 in), with an average length of 5 cm (2 in) velvet worms are segmented animals with between 13 and 43 pairs of legs.
Velvet worms come in a variety of colors, including brown, white, blue, grey, pink, and red. They share similarities with both arthropods (like spiders) and annelids (like earthworms), but are considered more closely related to arthropods, even though it was thought for many decades they were more related to annelids. More distantly, they are related to nematodes and horsehair worms.
Velvet worms are believed to have existed in their current form for an extremely long time, maybe as long as 430 million years, when the first animals took to the land. For much of history, velvet worms lived all over the Earth, not just in tropical regions. Fossils resembling velvet worms, called lobopods, have been found in Cambrian strata, up to 540 million years ago, demonstrating the lineage is very old. An early form, Hallucigenia, is one of the most fascinating organisms in the famous Burgess shale formation. Unlike modern-day velvet worms, Hallucingenia was covered in long spikes.
Velvet worms are carnivores with an unusual way of eating. They seek out prey (small insects) with their antennae, then barrage it with streams of sticky glue-like substance dispensed from hoses on their head. These streams criss-cross, like a lasso around the victim. In a single attack, a large velvet worm may use up a shot glass worth of sticky glue to trap their victim. The velvet worm has a waterproof body immune to the effects of the glue, so once the target is trapped, it just goes up and injects digestive juices into it, slurping up the dissolved victim. The glue also has a toxic effect that slows down the prey.
Because of their ancient ancestry, bizarre appearance, and unusual eating habits, velvet worms have proven to be popular exotic pets.