Why bats are the perfect hosts for viruses

The common horseshoe bat, Rhinolophus affinis, is a feat of biological engineering. The size of a small pear, it spends most of the day hanging upside down in dark, dank caves. To keep itself warm it huddles in tight colonies, wrapping its wings — which can measure up to two inches — around itself like a blanket. Even so, in winter its body temperature can fall as low as 43°F (6°C).

Then, two hours before sunset, it emerges to forage for insects using a horseshoe-shaped sonar dish on its nose to find its bearings. But now it has a new problem: flying requires so much energy that its metabolic rate can spike as high as 34 times its resting level, and its core temperature can exceed 104°F, causing cells within its body to break down and release bits of DNA.

Ordinarily, these cell fragments would cause inflammation, but thanks to bats’ weakened immune systems, they don’t.