Much like baby mammals nursing at the teats of their mothers, some baby jumping spiderlings are entirely dependent on nutritious spider milk secreted and fed to them by their mothers. What's more, spider mothers continue to care for and feed their offspring the nutritious milk-like fluid - which contains nearly four times the protein of cow's milk - into their subadult lives and long after they're able to forage on their own, a new study finds. According to the results, 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. For many animals, the growth, development and survival of young is wholly dependent on nutritious food often provided to them by their parents. 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. Zhanqi Chen and colleagues, however, describe strikingly similar, yet particularly puzzling, milk provisioning behavior in Toxeus magnus, a species of ant-mimicking jumping spider. 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. According to Chen et al., spiderlings remained in the nest and nursed on spider milk for nearly 40 days, shortly before reaching sexual maturity. Furthermore, the authors found that while nursing was not critical to offspring's survival after becoming independent, their mother's presence during their young lives greatly assured their overall health and adult survival. The mothers' nursing and care also seemed important for maintaining numbers of adult female offspring required for optimal reproductive success of the spider; although the mothers treated all juveniles the same, only daughters were allowed to return to the breeding nest after sexual maturity, the authors observed.
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Journal
Science