Diplura

Image: Michel Vuijlsteke

We're going back to the old school! Let's go out to the garden, turn over a stone and learn about a tiny arthropod that deserves at least a little bit of attention.

Forget about that centipede that escaped with startling speed the moment it was touched by the light. Never mind the busy ant's nest full of eggs you just unveiled. Ignore the unsettlingly human-like lower jawbone you just uncovered. Focus instead on the Diplurans, also known as Two-pronged Bristletails.

Diplura is an order of around 800 species of hexapod. Hexapod means "6 legs" and naturally almost all of them are insects. Diplurans, like Springtails, are one of the few hexapods that aren't considered insects.

Image: David R. Maddison

The main reason for them getting shunned and thrown into the outskirts of insect society is that their mouthparts are enclosed within their head such that you can't see them, while insects let their mandibles hang out. You get no points for table manners, I'm afraid.

If they have any friends among those stuck-up insects it's the Bristletails. The proper ones. Which happen to be "Three-pronged". They, and their close relatives like the Silverfish, are extremely ancient and have retained much of their ancestor's way of life, maintaining a deep distrust of modern society and new ideas like wings and colours other than brown and grey. Progress? Pah!

Aside from never evolving wings, Bristletails and Diplurans also share the same views on sex and childhood. They don't copulate, the male simply drops a packet of sperm for the female to pick up. The couple need never physically touch each other! Shame. They also lack metamorphosis. None of this "caterpillar and maggot" malarkey for them, their eggs hatch straight into miniature adults who are immediately sent to sweep out chimneys in true Dickensian style.

It's a stark life altogether for Diplurans. They live in the darkness and dampness of soil and leaf litter and since most them only reach 2 to 5 millimetres (0.08–0.20 in) long it's basically like living in a wet cave. As such, they lack eyes and are completely white, just like so many other troglobites. They feed on other dwellers of the underdark like mites, insects and spingtails, as well as fungus and detritus. Grim! I bet they don't put mattresses on their beds, either.

A lot of Diplurans have fairly long legs and are able to chase down their prey. Their cerci, the famous two prongs, are long and filamentous, are easily broken off but regrow over the next few moults. Others have them a little more short and stubby. And then there are the Japygids.

Image: David R. Maddison

Members of the Japygidae family are different from other Diplurans. Some of them can reach up to 5 cm (2 in) long for one, which is ten times bigger than most others. They also have shorter legs and more robust bodies. It looks like they won't be running after their prey. They'll need something else.

As we look from their pale, blind head and down their long, soft body, it's clear that their answer is to come to a violent end. Their cerci are brutal pincers that look like the back end of an Earwig or the front end of a termite soldier. They even have that orange and black colour which comes from sclerotisation, where the cuticle becomes harder and darker. Other athropodss have to do that all over whenever they moult, but Japygids only need that one violent and murderous part of their body to be tough as nails so they can use it to capture prey.

So it's the same old story we hear about many a killer. Pale and lank, wasting away in the dark poverty of their existence as they focus all their remaining energies into the one thing that proves they were ever alive: their ability to kill. Either that or it's one of those gray dwarves with his magic axe.