Jumping Spider Mothers Secrete Milk-Like Substance to Feed Their Offspring

A team of scientists in China has discovered that females of a species of ant-mimicking jumping spider called Toxeus magnus secrete a nutritious milk-like substance to feed their young. The discovery is described in a paper published this week in the journal Science.

Toxeus magnus, adult female. Image credit: Chen et al, doi: 10.1126/science.aat3692.

Toxeus magnus, adult female. Image credit: Chen et al, doi: 10.1126/science.aat3692.

Mammals produce their own nutritional substances, such as milk, and nurse their young until they learn to fend for themselves.

While lactation-like provisioning is known elsewhere in the animal kingdom, the intensity and duration of associated parental care is uniquely mammalian and thought to increase fitness by providing the opportunity for offspring to learn behaviors crucial for survival.

Dr. Zhanqi Chen from the Chinese Academy of Sciences’ Xishuangbanna Tropical Botanical Garden and colleagues discovered strikingly similar, yet particularly puzzling, milk provisioning behavior in Toxeus magnus, an ant-mimicking jumping spider species widely distributed in tropical and subtropical areas of Asia.

“It’s a puzzling observation for a species assumed to be noncolonial,” Dr. Chen said.

“It’s possible that the jumping spider might provide either prolonged maternal care or delayed dispersal. We decided to test it.”

Laboratory observations show the young spiderlings first drinking from droplets deposited on the nest’s surface and then directly sucking from the mother’s egg-laying opening.

“Closer observations revealed that the mother provided a seemingly nutritive fluid to the offspring,” the study authors said.

“Milk provisioning in Toxeus magnus involves a specialized organ over an extended period, similar to mammalian lactation.”

“Observations under the microscope showed droplets leaking from the mother’s epigastric furrow where the spiderlings sucked milk.”

The researchers found that the spiderlings ingest nutritious milk droplets secreted from the mother’s epigastric furrow until the subadult stage. If blocked from obtaining milk, the newly emerged spiders will stop development and die within 10 days, showing that milk is indispensable for offspring survival in the early stage.

Moreover, the team tested why parental care and milk provisioning were continued after 20 days when the spiderlings were able to forage for themselves.

The mother continued nest maintenance throughout, carrying out spiderlings’ exuviae and repairing nest damage. When receiving both maternal care and milk, 76% of the hatched offspring survived to adulthood.

“This newly identified and peculiar behavior compares both functionally and behaviorally to lactation in mammals and hints to the possibility that long-term, milk-provisioning maternal care may be more common in the animal kingdom than previously believed,” the scientists said.

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Zhanqi Chen et al. 2018. Prolonged milk provisioning in a jumping spider. Science 362 (6418): 1052-1055; doi: 10.1126/science.aat3692

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