Image: Ashlee Rowe
The sting of the venomous bark scorpion is painful, and thus serves as a deterrent to the arachnid's predators. But it seems to have the opposite effect on grasshopper mice - not only did the mice not feel pain, the venom actually works as painkiller to them.
Michigan State University researcher Ashlee Rowe, pointed out that the scorpion's venom can be quite dangerous. "This venom kills other mamals of similar size," Rowe said, "The grasshopper mouse has developed the evolutionary equivalent of martial arts to use the scorpions' greatest strength against them."
To test whether the grasshopper mice felt pain from the toxin, the scientists injected small amounts of scorpion venom or nontoxic saline solution in the mice’s paws. Surprisingly, the mice licked their paws (a typical toxin response) much less when injected with the scorpion toxin than when injected with a nontoxic saline solution.
“This seemed completely ridiculous,” says Harold Zakon, UT Austin professor of neuroscience. “One would think that the venom would at least cause a little more pain than the saline solution. This would mean that perhaps the toxin plays a role as an analgesic. This seemed very far out, but we wanted to test it anyway.”
Rowe and Zakon found that the grasshopper mice has a mutation in its sodium channels in the pain neurons. Instead of signalling pain, binding of the venom to that sodium channel actually blocks the pain neuron.
Watch as the repeated stings of the bark scorpion do not faze the grasshopper mouse one bit: