Milk comes from mammals. It’s kind of a distinctly mammalian thing. Even our government knows that. And yet, Chinese scientists have documented jumping spiders that provide their young with droplets of a nutrient-rich fluid from a furrow on the mother’s body. It is the sole nourishment for the spiderlings until they start foraging, and even then they still drink it until they get slightly more mature. Results are reported in Science.
Cockroaches and doves also provide their young with a substance described as “milk,” because it comes from their bodies and provides the exclusive source of sustenance to the young. Cockroach moms deposit this substance into the brood sac where their embryos are developing.
Dove parents—mothers and fathers both—generate crop milk and feed it to the baby birds for their first few days of life, until the babies can digest real food. Crop milk consists of nutrient-filled cells sloughed off in flakes from the inside of the parent birds’ crops, which are under their necks.