A crab’s scissors, stuck in a mousetrap, while there is no trace of the rest of the animal. Ecologist Roland-Jan Buijs donated his remarkable find, made along the facade of the Moerdijk Port Authority, to the Natural History Museum Rotterdam. The crab leg is unmistakably from a Chinese mitten crab (Eriocheir chinensis) because of the fur on the claw. It is known that this species can occur in strange places on dry land. They walk from the inland water to the sea where they reproduce. For example, on June 22, 1993, the Animal Ambulance rescued one from the track on platform 11 of Rotterdam Central Station. This migrant also became a museum piece.
The new acquisition, now with collection number NMR 9937-205215, intrigues me.
Just like in the movie ‘127 Hours’?
The crab scissors were not amputated by the mousetrap – the fracture surface is still in front of the clamp. Did the animal free itself, with its free scissors? Images from the film come to mind 127 Hours in which mountain climber Aron Ralston gets his arm trapped under a boulder and, after realizing that no one knows where he is, chooses the only survival option: he single-handedly breaks the bones of his forearm and excruciatingly slowly cuts through skin, muscles and tendons with a dull pocket knife. No fun, not even for the countless moviegoers who fainted or otherwise became nauseous during the self-amputation scene.
In the mitten crab, the constriction in the mousetrap caused less trauma thanks to autotomy: the ability to shed body parts during an attack or direct bite. Thanks to a subtle interplay of muscles on a pre-programmed fracture surface, salamanders, lizards and some species of mice discharge their tails, starfish release their arms, crickets release their legs and crabs release their claws. The goal is to escape and distract from a predatory enemy who is often left behind with a loose body part that is often still moving. There are even crab species that can attack their enemies thanks to autotomy.
Teddy bear as a test predator
The observation of a long-tailed otter that targeted a freshwater crab and screeched in fear as it retreated with a loose pair of scissors stuck in the fold of its neck, inspired three American biologists to investigate this behavior experimentally using a teddy bear as a surrogate predator. They did it in 1970 Science (!) report with Figure 1 showing a photo of the face of the plush animal full of crab claws. There were even species of crabs that sacrificed both claws at the same time when attacking the teddy bear. The good news for the crabs is that the claws are growing back. Mountain climber Aron Ralston was left with a prosthetic arm as a result of his self-amputation.