Last year, scientist Chen Zhanqi from China noticed a baby jumping spider behaving in a way that baby mammals do: it attached itself to its mother the way baby animals do when suckling milk.
Zhangi decided to closely study jumping spiders along with a colleague, and discovered that their babies actually do suckle milk from their mother's epigastric furrow, which is found on her abdomen. The milk was found to have four times the amount of protein as that of a cow, and the baby spiders suckled until they were considered "sub-adults" at 40 days old. But when the scientists painted over the epigastric furrow to block the flow of milk, the babies died after 10 days.
"Providing milk and long-term care together is virtually unheard of in insects and other invertebrates. And with the exception of mammals, it's not even that common among vertebrates," according to ScienceMag.org, which makes this discovery all the more fascinating.