When it comes to going the extra mile for your kids, there aren’t many mothers who can outdo the humble spider. From building silk nursery webs for their newly-hatched offspring to literally serving themselves up as their babies’ first meal, there’s almost nothing some spider species won’t do for their darling nightmare spawn.
Of course, they have an advantage – a 99-million-year head start. That’s according to a study published last month in the Proceedings of the Royal Society B, which looked at four chunks of amber from northern Myanmar and discovered something amazing: the oldest known evidence of maternal behavior in spiders.
“Adult lagonomegopid females probably built and then guarded egg sacs in their retreats or nests, and the hatched spiderlings may stay together with their mother for some time,” explains the study. “The evolution of maternal care is helpful for spiders in response to environmental pressures and represents an important step in the evolution of spider society.”
The now-extinct lagonomegopidae family of spiders lived in the mid-Cretaceous period, when Africa, North America, and most of Eurasia were still just one enormous supercontinent. Like many spiders today, it had two extra big eyes for hunting its prey; unlike many spiders today, those big eyes were on its side, rather than up front. When the dripping tree sap trapped the mother and spiderlings all those years ago, it preserved them so well that the researchers were able to use CT scans to pick out these tell-tale species markers and recreate the doomed arachnids in 3D.
"We expected that spiders had maternal instincts from their very beginning," study co-author Paul Selden told CNN. But the fossil evidence is “nevertheless, very nice,” he said, explaining "just how everything fitted beautifully into place. We had three or so specimens which all corroborated each other in the story."
Despite living nearly 100 million years ago, the behavior captured in the fossil amber is still recognizable in spiders today. One of the four pieces of amber studied, Selden told CNN, "shows a female lagonomegopid spider clutching an egg sac containing eggs about to hatch […] exactly how a living female spider which is nestled in a crevice in tree bark would look (in this case, right before being swamped with tree resin)."
The other three all contain newly-hatched spiderlings – along with some spider silk threads and fragments of leg, probably from the mother, the team says. That suggests mother lagonomegopidae would keep their children close for a while to protect them, like some spider species do today.
However, how long the spiderlings stuck around and how the species interacted after hatching remains mysterious for now.
“It is worth mentioning that mother spiders with offspring fossilized in amber represent a moment in time,” the study notes. “The discoveries of more similar fossils, especially if the offspring are in different [developmental stages], will add material for further study of maternal care and even potential social behaviour in spiders.”
Hopeful researchers will have to head for museum storerooms if they want to find those “similar fossils”, however – since the Tatmadaw took over the government of Myanmar in a military coup this February, paleontologists have been heavily discouraged from sourcing amber from the country. The four fossils used in last month’s study came from Capital Normal University in Beijing, where they had been since 2015.
Nevertheless, Selden said, the fossils are probably out there for anybody who wants to look.
“There are already thousands of specimens [in existing collections],” he told Science News. “And more material than there are people available to study it.”