Mother Spiders Actually Nurse Their Babies on Spider Milk

By | November 30, 2018

Jumping spiders are already among the most adorable members of the arachnid order, but we’re ready to give them the prize, officially. A species of ant-mimicking jumping spider has just been found suckling its babies on milk. You know what else does that? Kitties. Doggos. Mousies.

This is a high standard of infant care that had been thought exclusive to mammals.

“But ScienceAlert!” you are saying. “Spiders don’t have nipples!” (You may also be making some rude remarks about whether spiders can ever be cute. There are some people on our team who agree with you on that.)

While it’s true that spiders do not have nipples, it turns out that T. magnusdoesn’t actually need them.

The discovery was made by behavioural ecologist Chen Zhanqi of the Chinese Academy of Sciences and his team, who noticed some odd behaviours practised by the spiders.

Firstly, although these spiders are not known to form colonies, nests in the wild are often found containing a number of members, including grown juveniles. This caught Chen’s attention, and he brought some of the spiders into his lab for closer study.

And then, when the the babies did emerge, the third odd thing: a juvenile attached to a mother, like a young mammal at its mother’s teat – and the mother seemed to be tending to the baby in a caring way.

So Chen and his colleagues started to really take a closer look – and discovered that the mother was in fact producing a kind of milk for her babies. The stuff was nutrient-rich, containing nearly four times the protein found in cow’s milk, as well as sugar and fat.

Here’s how it goes. The mother spider lays a clutch of eggs, typically between 2 and 36. When the babies hatch, the mother deposits tiny droplets from her epigastric furrow, the opening on her abdomen from which she lays her eggs.

The newly hatched babies sip from these droplets from the first few days of their life; but as they gain a little bit of size and strength, they are able to suckle directly from the mother’s epigastric furrow.

But, although at about the 20 day mark, the spiderlings are able to leave the nest and start finding their own food, they continue to supplement their foraging with mother’s milk for another 20 days – a total of 40 days nursing.

In the lab, this resulted in a survival rate of around 76 percent. And it does look like the extended nursing time is crucial.

When Chen and his colleagues cut off the mother’s milk supply, spiderlings younger than 20 days died, while those older than 20 days were fine. Meanwhile, when the mother was removed entirely, older spiderlings tended to leave the nest sooner, didn’t grow as quickly, and were less likely to survive to adulthood.

The scientists aren’t sure exactly what the milk is made of, but suggest it could be liquefied, unfertilised eggs. Some other animals feed their young with unfertilised eggs – frogs, for instance, and bees, although generally the eggs are laid as per normal, and the young just eat them.

T. magnus‘ milk could be a similar source of nutrition, although supplied via a different delivery method. In fact, the duration of care she provides her babies is rare even in mammals, only seen in a few long-lived social species such as humans and elephants.

“The extended maternal care indicates that invertebrates have also evolved [this] ability,” Quan Rui-Chang of the Chinese Academy of Sciences toldScience magazine.

The team’s research has been published in the journal Science.

Studies Shows Spider Love On Its Babies

Jumping spider mothers provide milk to their spiderlings far into development, according to a new study that might turn your understanding of invertebrate parenting on its head.

Animals offer all sorts of provisions to their offspring, be it through regurgitation, unfertilized eggs, or in extreme cases, their own flesh. But specialized milk-like secretions are something erroneously attributed to solely mammals—other non-mammals and even invertebrates produce milk-like secretions, too. What’s exciting about this new study is not only the fact that spiders produce milk, but how long they provide it for.

“It sets up interesting questions about why this happens in the first place,” Nathan Morehouse, assistant professor at the University of Cincinnati who was not involved with the study, told Gizmodo. “Why are these spiders acting like college kids returning home to live with their parents?”

We often think about invertebrates as robotic beings that reproduce and eat and that’s it, but this is not really the case. Spiders care for their young in various ways—some just guard the eggs, while others will regurgitate food or lay unfertilized “trophic” eggs for newly hatched young to feed on. But jumping spiders providing milk presents an extreme case of invertebrate parental care.

The researchers behind the newest study, all from the Chinese Academy of Sciences, knew that Toxeus magnus or “jumping spiders” bred in nests that consisted of parents and several juveniles. They wondered whether the spider provided long-lasting parental care, so they observed some spiders in the nest. Then, they noticed that spiderlings didn’t leave the nest until they were around 21 days old, during which time the mother was never observed bringing back food while the young spiders grew larger.

A jumping spider
Photo: Rui-Chang Quan

They looked more closely and noticed that the mother was secreting a liquid from its upper abdomen onto the surface of the nest, which the spiderlings ate. After a week, the spiderlings sucked the milk directly from the mother. Even though they were able to leave the nest and feed themselves after 20 days, they continued suckling the milk for another 18 days. If these were humans, they’d be featured on a cable TV program. Once the spiderlings matured, the mother attacked the males that returned while females were still allowed in, perhaps to prevent inbreeding, according to the study published today in Science.

For those of you who have any doubts about the importance of the secretion, the researchers then blocked the mother’s milk glands with whiteout and the spiderlings died at 10 days old. When the mother was removed from the nest after 20 days, it reduced the overall survival of the baby spiders as well as their total size.

Scientists have observed other non-mammals producing milk-like secretions before, such as pigeons, cockroaches, and tsetse flies; earwigs also provide extended care to their young, said Joshua Benoit, also an assistant professor from the University of Cincinnati who was not involved with the study. He was impressed with and convinced by the research, but thought that maybe it’s time we rethink who we attribute nursing young to. After all, invertebrates make up over 95 percent of the Earth’s species.

“Production of milk-like system may have evolved more times in invertebrate systems than in vertebrates,” said Benoit.

The study has its limitations. It’s unclear whether jumping spiders in the wild—not confined to a lab enclosure like these were—would continue returning to the mother after 20 days, said Benoit. And Morehouse noted that it doesn’t really explain why these spiders continue nursing for so long, and why other spiders don’t produce milk. The study’s authors declined Gizmodo’s request for comment.

Reference

Some Spiders Actually Nurse Their Babies on Spider Milk

Spider Mother Gives Milk To Its Young Ones

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