Mesothele Spider

Image: Amir Ridhwan

The most ancient spiders in the world!

And no, it's not the giant, prehistoric spider that was the size of your head and could make a meal of your cat. The Mesothelae we're talking about may only reach lengths of 1 to 3 cm (0.4 to 1.2 in) but they have this amazing talent that very few creatures are capable of these days. They exist.

Turns out the giant, prehistoric spider was actually a giant, prehistoric sea scorpion. But they only found that out after they did a whole load of CGI and had it featured on Walking With Monsters. Whoops! Not to worry. It's actually heartening to know that we're still accumulating new, mythical beasts to add to the list.

Image: Amir Ridhwan
Mesothele spiders have HUGE palps near their mouth that look like two more legs

Our Mesothelae is a suborder of spiders with fossils dating back to the Carboniferous Period, some 300 million years ago. Today it's represented by a mere 90 or so species in the Liphistiidae family, all found only in southeast Asia, China and Japan. There are a few other families in the fossil record, but they're all extinct now. That's what happens when you rest on your laurels and forget to work on your existence skill.

Mesotheles are really clinging to life with two or three of their eight legs. Consider that there are only two other suborders of spider; the one with tarantulas and various trapdoor spiders with 15 families found all over the world but mostly in the tropics, and the one with all the serious web spinners that has 45 families living pretty much everywhere.

There are some 45,000 known species of spider. Less than 100 of them are Mesotheles.

Image: Amir Ridhwan
A male? They're smaller than females and have to walk around in search of a mate

Suddenly the Mesothele's Asian distribution looks like sunny retirement for the world weary. And as you might expect, they spend a lot of time doing nothing at all.

They're trapdoor spiders. They spend the day hidden deep in their burrows, a silk door covered in moss serving to camouflage their abode. They become more interested in food at night, which means they take an arduous journey to the mouth of their burrow and wait there instead.

Video: globalzoo

Any insect that wanders too close is liable to step on a carefully lain, silk tripwire. The vibration alerts the spider, and she swiftly emerges from her burrow, throwing open the trapdoor to grab her victim and drag it into the darkness of her lair. Most Mesotheles do all this in the forest, but there are a few cave species.

Here's something most unspider-like: it was long thought that Mesothele spiders had no venom! They have the fangs for it, but no-one could find any hole for venom to pass through. It wasn't until 2010, through looking very, very closely, that they finally discovered venom ducts in several species. They were between 5 and 10 micrometres long and situated along the length of the fang rather than at the tip. Then, with new confidence, scientists got the tweezers out and finally uncovered the venom glands.

Video: WildsidePhotography
Liphistius kanthan, found only in Kathan Cave, Malaysia

The other suborders of spider have much larger venom ducts near the tip of their fangs and much bigger venom glands for producing the stuff. So while at least some, if not all, Mesothele spiders have venom, there's still a question as to how effective it is.

Another example of strange, non-ideal placement involves the silk-producing spinnerets - they're toward the middle of the body rather than at the tail-end. It's just inefficient, you know? Certainly all those orb-web spiders would be like "I know a bad workman blames his tools but this is ridiculous!"

Image: Amir Ridhwan
Abdominal plates that don't quite cover anything

But the easiest way to distinguish Mesotheles from other spiders is the large plates that run down their abdomen. Spiders have rather soft abdomens which can expand after a big meal or when they harbour lots of eggs. The value of this is taken to an extreme in those plump orb-web spiders who waddle when they walk. They don't need to be particularly athletic since they don't journey around hunting prey, they just build a big web and have a go at injecting venom into anything that blunders into it.

Mesotheles still retain a bit of segmentation on their abdomen, which is why they're sometimes called Segmented Spiders. But the armour plates don't cover much, as if they're still deciding whether it's for protection or decoration. Just like all armour in all video games, ever.

Video: Spinnen in der Natur / Spiders in Nature
I find it hilarious how she opens the little door!

Aside from that, Mesotheles have a few characteristics in common with the tarantula group that the web-builders lack. They have long lifespans, like some of the tarantulas that can live for two decades. Most web-builders only live for about a year. Also Mesothele and tarantula fangs strike straight DOWN, unlike the web-builders who's fangs criss-cross.

Another example can be seen in their respiration. Mesotheles and tarantula types breathe using two pairs of book lungs. They look like books where each page is hollow and fills with air, while blood flows in between so oxygen can diffuse across. Most web-builders have replaced one pair of book lungs with a fine, branching network of air-filled tubes called trachea. This system is more efficient at bringing oxygen to where it's most needed and less liable to result in water loss. It means web-builders have been better able to expand into cool habitats that just aren't warm and humid enough for the others.

Image: Amir Ridhwan

So there's our poor, Mesothele spider, cooped up in her burrow, legs poised on her tripwires as she awaits the signal of food. Meanwhile enormous tarantulas stride along the ground and up trees, glorying in their magnificently potent venom. And tiny spiders construct astonishingly intricate webs covered in adhesive chemicals, as they babble on about how the silk-geeks have taken over and show off their "Science: it works, bitches!" t-shirts.

Yup... things have definitely changed.