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How the Scorpion Lost Its Tail (And Its Anus)

Many lizards can break off their tails when they’re in danger. Many spiders can do the same to their legs. This is called autotomy. The body parts have in-built lines of weakness that can easily tear, and the wounds tend to rapidly close and heal. Usually, the limbs grow back. The animal temporarily loses a bit of itself, which is better than losing its life.

But these trade-offs aren’t always so straightforward.

Camilo Mattoni from the National University of Cordoba in Argentina has discovered that a group of rare South American scorpions—the Ananteris genus—can also break off their tails. He has seen six species do so after he tried to grab them from behind with forceps; they wriggle furiously for a few seconds and then sever their tails after the second or third segments. In one case, the detached tail “writhed intensely, as if attempting to sting”.

Ananteris balzani losing its tail. Credit: Mattoni et al, 2015.
Ananteris balzani losing its tail. Credit: Mattoni et al, 2015.

As in lizards, these amputations are voluntary. If Mattoni anaesthetised the scorpions, or grabbed them by other body parts, the tail would never break.

The amputations are also common. Mattoni observed tailless individuals of eight more species, and he estimates that between 5 and 8 percent of wild Ananteris scorpions are wandering about with stumps instead of stings. They clearly survive the process—but they’re on borrowed time.

Here’s the problem. A scorpion’s anus isn’t where you think it probably would be. Instead, it’s at the end of the tail.

The gut extends all the way through the tail and opens up at the back of the fifth segment, just before the bit with the sting. So, when a scorpion performs autotomy, it leaves the final bits of its digestive tract writhing on the ground. And since the tail never grows back, that scorpion can never defecate again. Mattoni could actually see their abdomens swelling up thanks to the build-up of poo. In some cases, the increasing pressure forced another segment of the tail to break off, providing temporary relief.

The white stuff that you can see through the shell is poo. Credit: Mattoni et al, 2015.
The white stuff that you can see through the shell is poo. Credit: Mattoni et al, 2015.

To make matters worse, the scorpions lose the ability to defend themselves or to catch big prey. They still reflexively try to whack their targets with the stumps but their efforts are useless without the deadly sting. They are reduced to catching small prey with their pincers.

Despite these problems, the tailless scorpions can survive for around eight months. That’s plenty of time in which to find mates and reproduce. This probably explains why young scorpions never perform autotomy. They wouldn’t get the chance to reproduce before they died, so they’re better off trying other defences.

Females are also much less likely to self-amputate than males. Again, this makes sense. Females live longer, so they have more time to lose. They also have embryos to nourish, and they need their stings to catch larger prey. The males have no such needs and they can impregnate a lot of females in eight months. Better to do that, even if it means an abridged life without an anus.

Reference: Mattoni, García-Hernández, Botero-Trujillo, Ochoa, Ojanguren-Affilastro, Pintoda-Rocha, et al. (2015) Scorpion Sheds ‘Tail’ to Escape: Consequences and Implications of Autotomy in Scorpions (Buthidae: Ananteris). PLoS ONE http://dx.doi.org/10.1371/journal.pone.0116639

21 thoughts on “How the Scorpion Lost Its Tail (And Its Anus)

  1. Wait, I’m confused. So if the digestive tract goes all the way through the tail segments, I assume it’s an open tube, like a straw. When you cut off a fraction of a straw, the straw is still open. When the scorpion atotomizes part of its tail, does the wound just close up and seal over (cutting off the digestive tract)?

  2. Hi Zach, just one day after autotomy, a brown spot appeared medially, apparently produced by hemolymph coagulation, eventually darkening to form a blackish brown scar which completely blocked the digestive system, preventing defecation. You can see Fig. 2 in the article. 🙂

  3. I have seen grasshoppers sacrifice a rear leg – sometimes both to avoid capture( I catch them sometimes as food for my reptiles). Are grasshoppers capable of regenerating these legs as well?

  4. Don’t scorpions digest their food externally?
    I’ve observed that as they eat they leave white droppings.
    Does defecating through the tail apply to all scorpions or just specific kinds?

  5. Hi, Soly. Thanks! I just noticed the paper is PLoS ONE, which is great. I saw Fig. 2–I didn’t realize that hemolymph could coagulate!

  6. Thank for the information. I live on a farm-land where scorpions are quite common during the monsoon. I have seen them snap their tails off but never knew it affected their digestive tract too..

  7. I love nature. Simple and direct, no psycological myth of “feelings”. Natural law dictates! The law of the jungle prevails. Eat or be eaten. Life is a state of conflict. Rule or be ruled. Simple!

  8. A post-anal tail is a feature of chordates. In all other animals, the anus is at the last body segment, ie the end of the tail.

  9. Thanks for the information about the scorpion, This adds value to me as I am very much intereted in knowing the nature of animals. How long can the scorpion live?

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