Do spider moms nurse their children with milk? In a new study, researchers describe the mammal-like behavior of jumping spider moms as they were observed to care for their young even long after hatching.

Strange Spider Behavior

It was first in Singapore that researcher Zhanqi Chen observed jumping spiders of the toxeus magnus species engaging in strange behavior. Although toxeus magnus are not typically known to be social creatures, he would find a lone adult female surrounded by several younger spiders.

Observing the spiders back at the laboratory in Xishuangbanna Tropical Botanical Garden, Chen and his colleagues observed that the spiders stayed at the nest for at least three weeks after hatching. While neither they or their mother left the nest to look for food, the baby spiders still quadrupled in size in that period.

‘Lactating’ Spider Mothers

Evidently, the spiders still kept on growing because of the “spider milk” that their mother was providing for them. In the first week, the mother would secrete the “milk” from her birth canal and dabs it on the walls of the nest for her children to consume, but they soon begin to line up at the mother’s birth canal to directly feed. Interestingly, they would even supplement their diets with the milk even after they were able to hunt outside of the nest.

When researchers painted over the birth canal to cut off the milk supply, all the baby spiders died within 20 days. Similarly, when the mother was taken from the nest, the baby spiders grew slower, left the nest earlier, and were more likely to die before reaching adulthood.

‘Spider Milk’

So what is this spider milk? Upon testing, the researchers found that while it does not have a lot of fat or sugar, it had four times the amount of protein than cow’s milk. It’s possible that the unusual “milk” may actually be liquefied eggs passing from the birth canal, but what’s clear is that the baby spiders rely on the substance for sustenance even after they hatch.

Such maternal behavior can typically only be observed in social vertebrates such as humans, but the researchers’ observations show that even the invertebrates have evolved the behavior as well.

The research is published in the journal Science.

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