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Species:

Habitat: , loitering in gangs on rotting logs

Among proponents of non-lethal weapons, one of the most widely discussed technologies is ““, pioneered by Judge Dredd as . Fired from a high-powered gun, it rapidly solidifies on contact, immobilising the victims but – hopefully – not killing them.

As ever, nature got there first. Strange creatures called velvet worms use a similar trick to entrap their prey, and while the immobilisation process might not be fatal, the subsequent process of being eaten most certainly is.

Velvet worms are and are truly ancient: they were around in the Cambrian period over 500 million years ago, and were among the first land animals to take up walking. Nowadays there are about 90 species left, and ·¡.Ìý°ù´Ç·É±ð±ô±ô¾± is one of the most remarkable.

The worm that turned

They’re not your typical worms. For a start, they have legs – lots of them. The group is , but is , the group that includes insects and centipedes. In a bad light, velvet worms look like , and their brains are , a subgroup of the arthropods that includes spiders and scorpions.

What ·¡.Ìý°ù´Ç·É±ð±ô±ô¾± lacks in size – it is 1 to 3 centimetres long – it makes up for in naked aggression. The worms of around 15 individuals, nestled together in . The groups are dominated by the females, which and are . However, it is actually the males that start the groups, by which attracts females and other males to join them.

Not only do they live in groups, they hunt in packs. Their usual victims are small insects like termites, but they sometimes go for animals much larger than themselves, such as grasshoppers.

Once the prey is immobilised by , one of the worms finds a soft spot and injects the victim with saliva, which kills it and begins digesting its insides. While they wait for dinner to be ready, the worms eat the slime up again so as not to waste it.

When it comes to the main course, there is a strict feeding hierarchy, with the dominant female feeding alone for the first hour. Then other females are allowed to chow down, and finally the males and juveniles.

Slime time

So how does the riot foam work? of the research institute CSIRO Entomology in Canberra, Australia, and colleagues decided to find out by studying its chemistry.

Given that velvet worms are related to the arthropods, you might expect their slime to be similar to the silks produced by spiders and moths – but you would be wrong. Insects and spiders produce highly structured proteins, but the proteins in ·¡.Ìý°ù´Ç·É±ð±ô±ô¾±‘s slime are almost entirely unstructured and disordered.

As far as we know, the mechanism is unique, and it works something like this. The slime is mostly water, and because the proteins are disordered they expose a great many electrically charged regions to the liquid, ensuring that they stay fully dissolved as long as the slime is held in the slime glands.

But as soon as the slime is squirted – from limbs modified into sprayguns and mounted either side of the head – the water starts evaporating and the proteins start to come out of solution. This then triggers two mechanisms that trap the unfortunate prey.

First, the insect’s struggles pull some of the proteins out into threads that wrap around its body. At the same time, the loss of water causes the slime to transform into a hard, brittle solid: .

Readers who remember the resinous cocoons used to trap luckless humans in the movie may find this oddly familiar.

Journal reference: ,

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