Here's a horror with which to start your weekend. Multiple octopuses have been spotted engaging in autophagy — otherwise known as self-eating. They will consume their own arms, and no one knows why.

Many animals, including the octopus, will engage in a behavior called autotomy. The animal will break off a limb as part of a fight, to impress a mate, or to get away from a predator. It's a gruesome but understandable behavior. When biologists spotted octopuses that were missing limbs, they figured that autotomy was the cause.

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It wasn't even strange that octopuses missing limbs often died within a few weeks. Any grievous injury can kill an animal and not every survival strategy works long-term. Then scientists, and pet owners, and even aquariums saw their own octopuses lose their arms. Observation showed that the octopuses missing limbs didn't break their limbs off - they ate their own arms. Autophagy is not a survival strategy. Why was this happening?

At first, most people thought that the octopuses might be eating themselves because of a simple lack of food. Aquarium biologists believed that the octopuses in their care were well-fed, but some tried overfeeding just to be sure. Incidents of autophagy didn't stop. Perhaps, then, this was what happened when octopuses got bored or stressed-out. They ate themselves as a result of stressful captivity. But no amount of activity, or seclusion from the public, could prevent the behavior once it started. In fact, the behavior would often spread to any new octopuses in contact with the octopus that had started committing autophagy.

The best guess, today, is that this behavior is the result of some kind of infection — although people don't know what the infection is. The disease probably attacks the nervous system, causes the octopus to eat itself in a thoroughly horrible way, and then kills the octopus off.

Image: NOAA Photo Library:

[Source: Autophagy in Octopus.]