What ancient invertebrate can breathe through its skin, squeeze through tight spots, and use slime to attack prey?
The velvet worm!
Have you heard of the velvet worm? Technically not a worm, this funky invertebrate actually has little legs – up to 40 or so, and is crawling its way into the (strictly metaphorical) spotlight. (They actually thrive in dark and damp environments.)
Native to the tropics and some temperate regions around the globe, these creatures inhabit the forest floor, where they can be found among the leaf litter, under stones or fallen logs, inside termites’ nests, or burrowed into the soil as deep as three feet (~ 1 meter) below ground. Though they have soft, velveteen bodies as their name suggests, reaching out to touch these creatures is discouraged, as it could harm the velvet worm and land a curious human in a sticky situation.
The velvet worm actually breathes through its skin, and having a moist environment is crucial to its survival. They risk drying out if not enough moisture is available, and they avoid bright areas for this reason. Velvet worms take in oxygen across the body’s surface through a diffusion process, and have small tubes (or tracheae) that bring that oxygen to organs below the surface.
Velvet worms have hydrostatic skeletons, which essentially means that their body cavities are controlled by the flow of pressurized fluids that allow sections to expand and contract. With flexible skin and no rigid bone structure, these invertebrates are able to squeeze into extremely small cavities. They also possess plenty of impressive abilities, from reproductive adaptations featuring more amazing absorption to some Spider Man-style predation.
Ancient (pan)arthropods
There are over 200 species of velvet worms that make up the phylum Onychophora. Though they vary in color, sporting shades of blue, gray, brown, or purple, these creatures share an appearance similar to a caterpillar, or a long, soft-bodied worm with legs.
In fact, their physiology led scientists to hypothesize that velvet worms played a role in evolutionary history linking arthropods (like crustaceans and insects) with annelids (segmented worms). Nowadays, velvet worms are considered part of the taxon Panarthropoda, along with another personal favorite, the Tardigrade.
These creatures offer a glimpse back in time that both challenges our classification systems and provides insight on conditions during earlier points in Earth’s history. Velvet worms’ close relatives have dated back around 500 million years to the Cambrian period. Their fossil records also show a distribution across the globe that includes regions of the Northern hemisphere where warmer temperatures and humid, tropical-like climates would have allowed velvet worms to thrive.
Remarkable Reproduction
The velvet worm has many tricks up its sleeve when it comes to reproduction. Nearly all species reproduce sexually, which involves mating processes with different degrees of complexity. Some stick with the basics, in which spermatophores from the male are deposited directly into the female’s genital opening. However, in other species, spermatophores are deposited on other parts of the female’s body, after which they are absorbed into the skin and internally migrate to the ovaries to fertilize an egg.
Female velvet worms can actually store sperm for months on end before using them to fertilize an egg, building in a delay to the reproductive process that may be useful under adverse conditions. They generally give birth to live young, but some species lay eggs instead.
Most notably, one species (Epiperipatus imthurni) exhibits the astounding phenomenon of parthenogenesis, in which an all female population is able to reproduce asexually, and no male individuals have been observed. Talk about girl power!
Super slime
My personal favorite feature of the velvet worm is the slimy substance it uses to subdue its prey (or occasionally release in defense). Velvet worms hunt at night as ambush predators, approaching their victims and squirting out a fast-drying adhesive liquid that traps prey in place, an important advantage when the worm itself is slow moving.
When ready to feast, the velvet worm bites into its prey and injects a saliva that liquifies the insides for easier consumption. In this way, velvet worms subsist on a diet of other small invertebrates, including woodlice, crickets, termites, cockroaches, and larger creatures like worms and snails. Though this somewhat gruesome technique may make the velvet worm seem like a fearsome foe, they only eat every one to four weeks, depending on their size. After all, it takes a good deal of energy to go through such an intense hunting process.
Check out this tactic in action:
The slime itself is made up of water and a concentration of proteins, and velvet worms have been observed shooting it up to a foot (~30 cm) in distance. Its stickiness, stretchiness, and tensile strength (resistance to breakage) make this substance the subject of great interest. In fact, some scientists at Nanyang Technological University in Singapore are studying velvet worm slime for insights on creating biodegradable materials to replace plastic.
While the threats and conservation status of different species of velvet worms vary by location and population, these creatures need intact biodiverse forest ecosystems to thrive. As we work to protect and restore forests and wetlands, we can think of these creative crawlers and continue to learn about the living treasures all around us.
With that I’ll wriggle away.
By Maya Dutta
Sources:
https://en.wikipedia.org/wiki/Onychophora
https://www.britannica.com/animal/velvet-worm
https://www.wired.com/2014/03/the-creature-feature-10-fun-facts-about-velvet-worms/
https://australian.museum/learn/animals/worms/velvet-worm/
https://www.wettropics.gov.au/the-velvet-worm
https://www.nationalgeographic.com/animals/article/150317-velvet-worms-animals-slime-science
https://www.ntu.edu.sg/news/detail/velvet-worm-s-slime-could-hold-the-key-for-sustainable-biodegradable-bioplastics