The wild world of Velvet Worms!

On this week's episode we look at the animal that bridges the gap between worms and insects. Velvet worms are incredibly unique for a number of reasons and in this episode we cover everything you'd want to know about why these worms are so cool. 

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Featured Artists: Jordy Chandra, S N U G, Purrple cat

 

Transcript: 

 

Welcome back everyone to another Tuesday where we dive into something Entomological, except today is a little different (insert sound effect). We have a listener submission from Owen out in England wanting to learn more about the Velvet Worm, and after seeing them I wanted to learn more too. 

 

Velvet worms are in the class called udeonychophora which are worm-like and caterpillar-like animals from an ancient time that still exist today! Their appearance has changed very little over the past 500  million years, and they are considered to be a link between arthropods and annelids. For those that need a recap, annelids are worms. 

 

Anyway, there are about 230 known species for these fellas and those are divided by two families. Unfortunately for many of us, finding these animals is not an easy feat. because they’re only found in sporadic geographic locations. For example the family Peripatidae can be found from Central America to the bottom of Brazil, and select countries in the east like one island of Indonesia, Thailand, Malaysia, and one country in Africa, and the other family known as Peripatopsidae can only be found in New Zealand, Papa New Guinea, select parts of Australia, one location in Chile and Lesotho South Africa. If you’ve ever seen one in real life and have a cool story about it, definitely hit me up on IG or FB cause I wanna know about it. 

 

So these not-quite worms and not-quite arthropods are super cute, and they have some interesting features as well. So let's jump into the description but pictures of course will be available on the IG and FB page (links to those in the description). 

 

Velvet worms have a segmented body, but it's long and cylindrical with stubby appendages called oncopods or lobopods which they use to traverse their environment. 

Think of these worms as like a cross between a soft caterpillar and a centipede but with max cuteness. The average length for these is around 5cm or 2inch but they can be as long as 20cm or 8inch and as short as 0.5cm or 0.2 inches, and they come in a variety of crazy colors like blue, red, orange, gold, blue AND orange, I mean seriously what more could you want.  

 

The heads have two antennae and two simple eyes (unless a blind species), and a circular mouth that sits belly side of the head and as a result you would never know they had a mouth unless it lifts its head.

The amount of feet these worms have is dependent on the species, 

 

but a really unique feature for all of them would be the hard chitin claws they hide within these soft stubby feet. 

 

This is actually where the name Onychophora comes from because the ancient Greek means claws. Don’t worry though! These claws have one purpose only and that’s to help them stand their ground while crawling around. These claws actually have 3 layers to them and fit inside each other like Russian nesting dolls, and the outermost layer can be shed.

 

They also have two pairs of claw-like mandibles hidden in their mouths. One is more external and the other is further back. The external ones move purely through muscle usage but the internal ones move through hydrostatic pressure. In fact, the whole body gets its locomotion from hydrostatic pressure changes. Now for us non engineer people, hydrostatic pressure refers to the pressure a liquid creates on the outer edges of a confined space. This is where blood pressure gets its name from. 

 

As for why these worms are called velvet worms has to do with the soft and velvety texture of their bodies. The skin of these worms is covered in small bristles known as papillae which are sensitive to both touch and smell. We have papillae too, on our tongues, which for us are used to taste, and grip food. The papillae on velvet worms are actually covered in small scales of chitin and this is actually water-repellent as well. Despite the skin being water-repellent and very elastic it does have a problem, and that would be the inability to control when water escapes the body, and as a result, these worms need to live in areas that have high levels of moisture which explains their very sporadic geographic range. 

 

Now I wanna backtrack a bit about the claw-like mandible, because as it turns out these cute worms are not very cuddly. In fact, they are quite ferocious, and prey upon smaller invertebrates like spiders, woodlice, beetles, and termites. One species even hunts in a group like a pack of wolves. As for how they can even catch the prey, that comes down to their special slime glands on either side of the head. You see, kinda like spider-man, these worms can eject threads of sticky slime and they use this to trap prey and halt predators.

 

The worms can’t directly aim the strands of slime though, and instead rely on the fact that the speed of ejection causes the glands to inflate and rotate creating a spiral of sticky goo that can ensnare prey and predators from up to 2 feet away. It gets even crazier though because the slime itself is fast drying, and hardens causing the targets to freeze in their tracks. The entire process is also extremely fast happening under a second. 

 

The worms are not very well equipped at sight though and it really doesn’t do them any favors that they primarily feed at night too. Because of these reasons they rely on vibrations in the air, and once a prey item is located they actually sneak up and poke it repeatedly for extremely brief moments to try and analyze the size and whether it's worth it or not. The worms start their hunts around dusk and continue until dawn, at which point they need to retreat and find a moist shady place to hide. That being said, if its a rainy day then it is possible for them to do their thing during the day. 

 

Earlier I mentioned that one species hunts in packs and I wanna dive into that a bit, because the specifics on it are kinda wild. The species is called Euperipatoides rowelli and it's found in Australia! This species holds a matriarchy lead by the most dominant female. Essentially hierarchy is formed by females annoying each other by poking and prodding with their antennae. The female who can tolerate the most. This species lives together in groups up to 15 individuals, and the larger the group the faster the foraging is completed. Feeding is prioritized by rank, so the head female gets first dibs and feeds alone followed by the other females, males and the young in that order. 

 

When it comes to reproduction, almost all the species reproduce sexually, which means there is a need for males and females. They are also sexually dimorphic with females usually being larger than males. By far the most interesting details about their reproduction are in the methods that different genera use. For example in the genus peripatus, males will actually leave a package of sperm known as a spermatophore on the back or sides of a female and then Amoebocytes from the female's blood actually collect at that location and break down the skin wall and sperm package allowing its contents to be absorbed into the body. That’s insane! Another wacky method would be the use of head structures to deposit spermatophores into females which can be seen with Australian species. Traditional copulation doesn’t seem to be a commonality for these worms, but then again, these velvet worms are far from normal. 

 

When it comes to giving birth the females have three different strategies. 

 

The first is your standard egg laying which actually only occurs in the family Peripatopsidae and this also happens to be the more primitive family as well. 

 

The second and most widely used strategy is known as ovoviviparous and this refers to the process of incubating eggs within the body until they are ready to hatch! 

 

And last but not least some velvet worms do indeed give live birth! This occurs in both families but seems to be more restricted to areas that provide a stable climate and food source year round. 

 

The amount of offspring a velvet worm can produce in their lifetime caps at around 23, and they only mate once! In fact, because they only mate once for the entirety of their life, they have special organs dedicated to storing sperm, and some females can mate before sexual maturity and just store the sperm until they’re ready to reproduce. 

 

Now before we end today’s episode there is some hope to those of us who would like to see one in the flesh, because as it turns out these worms can be purchased as pets online or even in certain pet stores. If you wanna try your hands at keeping one of these wild worms I’d certainly recommend it as they are very cute, and easy to care for. The lifespan for these can last up to 6 years, and based on the size of the food and worm they only need food once per week or per every four weeks.