Zebras, bats, and bears do it. So do whales, tigers, and humans. These animals all nourish their newborn offspring with milk. It’s a defining characteristic of what it means to be a mammal.

According to a study published today in the journal Science, a jumping spider native to southeastern Asia does the same thing. Toxeus magnus has been found to suckle its babies with a nutritious fluid secreted by its own body. The liquid contains a solution of sugars, fats, and proteins, so the researchers, led by conservation biologist Rui-Chang Quan of the Chinese Academy of Sciences, are calling it milk.

Perhaps most surprisingly, the researchers found that spiderlings continue drinking their mother’s milk even after reaching sexual maturity. “That's