https://motherboard.vice.com/en_us/article/wj3gv9/this-jumping-spider-makes-milk

Got milk? If you’re a special species of jumping spider, the answer is yes. That’s what scientists discovered when they observed female Toxeus magnus spiders nursing spiderlings with a milky substance for several weeks.

The finding, published Thursday in Science, suggests that despite milk’s strong association with mammals—a group named for its lactating mammary organs—nursing behaviors may be widespread in organisms that we wouldn’t think of as breastfeeders.