Spider Milk. Yep, you heard that right.
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?
Read the actual research paper Prolonged milk provisioning in a jumping spider
Detailed illustrations of Toxeus Magnus Survey of the genus Toxeus