A glance at the picture of his adopted bat stopped me in my tracks. It showed a bat with a scorpion in its mouth! Bats eat scorpions? How is that possible? Bats eat flying insects, right?
After reading the scientific literature on Antrozous pallidus and looking at the Bat Conservation International website, here’s the pallid bat’s story. It’s far weirder than I imagined.
Pallid bats live in the western United States and are the size of a sparrow but with the wingspan of a crow—though they are of course mammals and not birds.
Their big wings allow them to hover and catching their food on the ground. They have large ears that can hear the footsteps of a scorpion or centipede (another favorite food).
The bats appear to be immune to scorpion stings from even the most venomous scorpion in North America, the Arizona bark scorpion. Up to 70% of a pallid bat’s diet can be scorpions at certain times of the year.
But how does a bat find a scorpion at night on the ground given that the sounds from a scorpion’s feet are rather minimal?
Like many small bats, pallid bats use echolocation, a kind of bio sonar, to “see” in the dark. But weirdly, pallid bats stop using their sonar when they attack prey on the ground.
So what do they use to guide them in for a pinpoint pickup of a fleet-footed scorpion? Is it just their sensitive hearing, or might it also be their eyes?
Pallid bats have unusually large eyes for a bat, and several species of bats are known to be able to see ultraviolet light. Might the pallid bat also see ultraviolet light? My hypothesis is that they do. Scorpions, and to a less extent centipedes, fluoresce brightly under a ‘black’ light.
So pallid bats might use ultraviolet light to zero-in on dinner. But this presents an evolutionary problem. If pallid bats spot scorpions by their florescence, why has this characteristic not been deselected in scorpions?
After all, the scorpions get eaten if they are caught by the bat. The fluorescence appears to allow scorpions to find shelter quickly. A recent study found that the body of a scorpion is like a giant proto-eye that can sense ultraviolet shadows even in the dark. It’s what helps them find any nearby hiding place quickly and save themselves from a predator. Perhaps it’s a scorpion’s fluorescence helps against more numerous enemies than a few super-powered bats.
When the weirdness is added together what we have is a scorpion-eating flying mammal that’s immune to scorpion stings, can hear the rustle of a scorpion from a distance, can hover above the ground, has echo location but doesn’t use it when attacking scorpions, and may be able to see the ultraviolet light that scorpions reflect. Bats are amazing creatures.