Whether you think spiders are cool or you think they are scary, there is one thing that almost nobody would call spiders. Good parents.

For the most part, a spider lays its eggs and then either abandons them entirely, or  guards the egg sac until they hatch and then the baby spiders are off on their own.

For the ant-mimicking spider (Toxeus Magnus), however, that is apparently not the case. When a mom lays eggs, she stays around them until they hatch. The clutch of baby spiders then stay near the mom, who produces milk.

Well, it isn’t exactly milk like you would see with mammals, but it is a nutritious liquid that the baby spiders can’t live without. So, if we can call almond milk milk, we can certainly call this milk as well.

This isn’t just a little sip of milk to get the spiders started either. She will feed them this way exclusively until they are nearly adults, well beyond the point where they are actually big enough to forage on their own. A paper was written on this behavior in 2018, which explained:

“The spiderlings ingest nutritious milk droplets secreted from the mother’s epigastric furrow until the subadult stage. These findings demonstrate that mammal-like milk provisioning and parental care for mature offspring have also evolved in invertebrates, encouraging a re-evaluation of their occurrence across the animal kingdom, especially in invertebrates.”

This came as a surprise to the scientists who study this spider. They initially noticed that the breeding nest didn’t look like the nest of other spiders. They found that there were usually a few adult spiders as well as multiple juveniles. Once they saw this, they took some spiders back to their lab so they could monitor them much more closely, which is how they discovered this unusual trait.

It is believed that this is an example of convergent evolution, which is where a similar trait evolves in different species that are unrelated. The study authors explain:

“In nonmammals, we suggest that the most important ecological conditions favoring the evolution of lactation might be predation risk and uncertain food access. As a response, the mother’s physiology, behavior, and cognition might have changed to adapt to providing milk and prolonged maternal care as in mammals. Extended parental care could have evolved in invertebrates as a response to complex and harsh living environments that require offspring skills (e.g., hunting, predator defense) to be fully developed before complete independence. Another aspect to investigate is whether lactation and extended parental care are accompanied by a reduction in offspring number because of milk production and parental care costs.”

This is quite an incredible find and may encourage researchers to take a closer look at other spider species as well as other animals that are traditionally assumed not to care for their young.

If you thought that was interesting, you might like to read about why we should be worried about the leak in the bottom of the ocean.