Toxeus magnus male. Image: Wikimedia CC

Scientists in China have revealed that one species of spider nourishes its newborns with “milk” — a behavior typically only observed in mammals.

Toxeus magnus, an ant-mimicking jumping spider native to southeast Asia, secretes a highly nutritious milk-like fluid containing sugars, fats, and proteins to keep its young alive. The substance contains four times the protein of cow’s milk.

Initially, the spiderlings slurp up milk droplets that the mother leaves around the nest. Once they become large enough, the young crawl directly onto their mother and suckle straight from her epigastric furrow, the egg-laying opening that doubles as a milk dispenser.

Scientists found that the spiderlings suckled exclusively for at least 20 days, then used the milk as a supplement while they left the nest and learned to forage. All spiderlings were given the right to suckle until they reached subadulthood at around 40 days, but only females were allowed to suckle longer, nursing well into the time they reached sexual maturity. Males that tried to return to the nest to suckle were attacked by the females and forced to leave.

Lactation has long been considered almost exclusive to mammals — instances of non-mammalian creatures producing a milk-like substance to nourish their offspring are rare. But researchers hope the findings will lead others to search for maternal behavior outside the mammal class.

“Our findings demonstrate that mammal-like milk provisioning and parental care for sexually mature offspring have also evolved in invertebrates,” said Dr. Zhanqi Chen, lead author of the study, published in Nature. “We anticipate that our findings will encourage a reevaluation of the evolution of lactation and extended parental care and their occurrences across the animal kingdom.”

Experts believe that the species evolved this capability due to the lack of food available to young spiders, as well as the prevalence of predators surrounding nests. Genius!