“Finding such mammal-like behavior in a spider, or in any invertebrate for that matter, was a surprise,” said Richard Corlett, a conservation biologist at the Chinese Academy of Sciences and an author of the study.

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Jumping spiders are the single largest group of spiders in the world, with more than 5,000 species and a presence on nearly every continent. The tiny T. magnus, also known as the black ant mimicking jumper, looks like an ant, walks like an ant and even waves its front legs in the air like a pair of antennas (it jumps when threatened or hunting). The species is found mostly in Southeast Asia.

The study came about after the lead author, Zhanqi Chen, also of the Chinese Academy of Sciences, noticed that young T. magnus seemed slow to leave the breeding nest, suggesting the mothers were providing some sort of extended child care. That hypothesis received a boost when he and his colleagues observed newborns in the lab and found that neither they, nor their mother, left the nest to find food for the first 20 days.

Looking closer, they found that during the first week, the mother was depositing droplets of fluid from her underside onto the nest that the hatchlings would come and drink. After the first week, the offspring would drink the fluid directly from the mother’s body.

Adding to their surprise, the researchers found that the mother continued to provide the fluid even after her young began leaving the nest to forage at about 20 days old. The suckling finally ceased at 40 days, though the offspring still used the nest at night for another 20 days.