Female vampire bats donate blood to friends to ensure their survival down the road—suggesting the animals' social lives are much more sophisticated than we thought, a new study says.

The findings shed further light on the often maligned species, which is native to the American tropics. Vampire bats eat only blood—taking small amounts without harming their hosts—and have amassed remarkable biological hardware to do so. They can sense body heat like a pit viper, run and jump surprisingly well, and urinate half of their blood meals’ water content within 30 minutes of eating.

They also live in tightly knit communities in which multiple unrelated females regularly band together, perhaps providing their pups—and each other—with body warmth and protection