In the North American southwest, pallid bats emerge at night to stalk the skies, listening with their large ears for the sounds of scuttling prey. They swoop down on all sorts of insects and sometimes even small lizards and mice – but you might think the Arizona bark scorpion, armed with the most dangerous scorpion venom on the continent, would be a meal too far. And yet, surprisingly, the bats don't seem to mind the arachnids' normally painful sting.

Researchers in California were impressed enough by the bats' hunting mettle to investigate just how the species survives its tangles with such dangerous prey. At around eight centimetres (three inches) long, the scorpions are roughly the same size as the bats themselves, and their sting is known to cause extreme pain and death in other animals, including mice and sometimes even humans. The bats, it seems, are immune.

High-speed cameras revealed the slow-motion details of a bat hunt. As the bats swooped down to attack the scorpions, they made no attempt to avoid the retaliatory stinger strikes. "Our results show that the pallid bat is stung multiple times during a hunt without any noticeable effect on behaviour," the scientists describe in their paper in PLOS One.

"Even direct injection of venom in this bat in known doses has little effect on its behaviour," said Khaleel Razak of the University of California, Riverside, in a press release. Delivering doses of the venom to lab mice causes convulsions and disorientation in the small mammals, but when several pallid bats were given the same venom injection, some at quite high doses, they showed for the most part no reaction at all.

Being resistant – mostly or totally – to scorpion venom is a great asset for a hungry hunter, but where this resistance comes from is a mystery. Since the toxins in the scorpions' venom target their victims' dorsal root ganglia (clusters of nerves in the spine) and interfere with their pain pathways, they can cause severe agony. But when the researchers explored the bats' genetic code, they found that this species has developed mutations to the regions the venom toxins normally latch onto, a unique defence that leaves the bats free of pain ... and free to eat all the scorpions they want.



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