D: Yaël, isn’t it only mammals, such as cows and human beings, that produce milk to feed their babies.

Y: No, Don. There are also some insects and spiders that produce a milk-like substance to feed their young. Don’t you remember when we talked about cockroach milk?

D: Yuck! That’s something I would prefer to forget.

Y: There’s more. In 2018 a team of Chinese scientists discovered a species of jumping spider that secretes milk to feed its offspring. The milk has four times as much protein as cow’s milk. The spiders are more like mammals than cockroaches, because they give milk to their offspring over a prolonged period of parental care.

D: Really? How do they care for them?

Y: When the baby spiderlings first hatch, they completely depend on their mother’s milk for nourishment. She secretes droplets of the milk onto the walls of the nest for them. After about the first week of their lives, the babies start to suck milk directly from their mother’s body, much like a mammal would nurse. The researchers could watch could watch under the microscope as the milk droplets leaked from the mother’s body during this feeding. The researchers know that the babies depended on the fluid, because if they blocked the mother’s milk opening, the babies died.

D: That does seem a lot like a mammal. When do the young spiders start catching prey on their own?

Y: The young spiders start leaving the nest to forage at about twenty days of age. But they also continue to drink their mother’s milk until they are about forty days old and almost sexually mature.