Spider Milk. Yep, you heard that right.

アリグモ ant spider” by merec0 is licensed under CC BY 2.0


So, let’s clear out some terms here.

Mammals are mammals because they produce milk.

Milk is a nutritious liquid to provide for the young. It contains essential nutrients for nourishment and antibiotics to help with the immune system.


What if I said that spider milk exists? Ready to call spiders mammals?


Toxeus Magnus is a species of Jumping spiders native to Southeast Asia with a distinctive ant-like appearance. A group of scientists led by Dr. Quan of the Chinese Academy of Sciences was studying them when they discovered the baby spiders growing bigger without eating anything!

Dr. Quan examined them more closely, and to his surprise, he saw the mother secreting liquid droplets on the nest floor, and soon after, the spiderlings gathered to sip them. After the first week, the spiderlings obtained the liquid straight from their mother by clinging on to her.

Investigation of this liquid told us that it contained sugar, fat, and protein. Same as cow’s milk! And even crazier, they were found to be a lot more nutritious than cow milk. Spider milk contained less sugar, less fat, and 4 times more protein than cow’s milk.

In an alternate universe where we could magnify the amount of spider milk, we could be drinking it right now!


What is spider milk?

So, what is this magical milk made of? Since the liquid is produced from the opening where the mother lays its eggs from, Dr. Quan suggests it is very likely that it was made from recycled unfertilized eggs.

To test if the milk was an essential source of nutrients for the spiderlings, Dr. Quan did an experiment where he glued an opening on the mother spider from where she produced milk. Without access to the milk, the spiderlings died within 11 days. Milk is a necessity to spiderlings just like human babies. 

Spiderlings depend on their mother’s milk for up to 20 days. From then, only the daughters could continue drinking the milk even after reaching sexual maturity.

Female spiders are a lot more cherished in the spider community. Female adult spiders are allowed to come back home, but the male spiders would be kicked out if they ever tried to come back. Poor guys.

This is because these spiders spend energy on maternal care and so, increasing the female population is beneficial to the growth of spider communities. Also, by kicking out the boys it could prevent inbreeding (mating of individuals that are genetically closely related) which could lead to uncompetitive offspring.


What are spider mums like?

Spider mums are very nurturing. Some of them regurgitate food for their babies, guard their eggs on an empty stomach, and crab spider mums liquefy themselves so that they can become food for their kids.

With these extreme maternal behaviors, it makes sense that a spider species would evolve to provide nutrients in the form of milk for their young.

Interestingly, the presence or absence of maternal care determines the sex ratio. When maternal care was present, there was a higher ratio of female offspring, again relating back to the benefits of having more females.

Jumping spiders are the first-ever non-mammalian animal to have ever been found to provide both extended maternal care and provide milk.

These findings has made me question the terms used to describe animals. Maybe it’s time to change it up.

What did you think?

Should we be calling spiders mammals?


Further readings

Read the actual research paper Prolonged milk provisioning in a jumping spider

Detailed illustrations of Toxeus Magnus Survey of the genus Toxeus

15 Responses to “Spider Milk. Yep, you heard that right.”

  1. mbalia says:

    Fascinating post Kiena. I’m not sure I’d be ready to welcome to welcome spiders into the mammal family, maybe we could focus the definition of mammal a bit to make it more accurate?

  2. Keina says:

    Thanks awaskowicz, I’m glad I got to share something new!

  3. Keina says:

    glad it was okay Wayne!

  4. awaskowicz says:

    This post taught me so much I never would have guessed about spider behaviour! Really fascinating, informative, and well written 🙂

  5. Wayne Du says:

    It’s all good, the image you chose was great, didn’t scare me too much (I just imagined it as an ant).

  6. Keina says:

    Thanks for the feedback Wayne, I hope my post didn’t make you feel uncomfortable, I certainly was when I was searching for photos of spiders!

  7. Keina says:

    Thanks sgiarusso, I didn’t know that most spiders were nurturing either. Maybe we need a reclassification of the terms, milk, and mammals for things to make more sense since we are discovering more and more each year.

  8. Keina says:

    Thanks bssa, it would be very cool if Toxeus Magnus could be classified as a mammal, they’d be very special amongst the spiders:) But I’m sure there are other spider species that also produce milk and provide maternal care, we just haven’t discovered them yet!

  9. Keina says:

    Thanks Isobel. That’s a good point. Toxeus Magnus may produce milk but we wouldn’t be able to say that they produce mammalian milk.

  10. Keina says:

    Thanks Nithin, I was very surprised too when I stumbled across this and I had to share this with everyone! Cockroaches also produce milk, but their not quite as close to mammals than the Toxeus Magnus species since they are not known to demonstrate maternal care.

  11. Wayne Du says:

    Hi Keina,
    I thought this piece was great. You definitely know how to grab your audience’s attention, even mine (the most arachnophobia person in the world). I thought your title was great and the way that you started of clarifying your terms was really smart. You also did a great job of explaining the study by Dr. Quan and definitely did a good job of picking out the important points!

  12. sgiarrusso says:

    I loved your post! I always thought spiders laid their eggs, hung around for a few days after they hatch, and then left them to fend for themselves.

    I don’t think spiders can be taxonomically changed from Arachnida to Mammalia though, just because they produce ‘milk’. Platypus are egg-laying mammals, and I don’t think they’ll ever be classified as Aves or Reptilia.

    There’s almost always an exception to the rule, but your post is super interesting none the less! Well done 🙂

  13. bssa says:

    This was informative. I never knew that this species of spider could provide milk and maternal care for its young. Maybe just the Toxeus Magnus can be classified as a mammal, but not any other spider.

  14. Isobel Beasley says:

    I don’t think I’d ever call spiders mammals! I’d like to say that’s because spiders don’t have mammary glands and mammals are defined by their glands, but actually, it’s probably more to do with my own dislike of them!

  15. Nithin says:

    This is such a fascinatingly gross topic, I love it. Would have never thought spiders would be one of the first things we find outside of mammals to produce milk. Though I’m now slightly concerned about someone advertising Spider Milk as the new superfood or dairy substitute. A great post, thanks Keina!