Modern-day female spiders have a remarkable maternal instinct. The eight-legged mothers are known to guard their egg sacs by either carrying it in their jaws or attaching it to their silk-spinning organ called a spinneret. Thanks to four prehistoric spider-moms trapped in amber, scientists now know the behavior evolved millions of years ago, according to a new study published this week in Proceedings of the Royal Society B.
The quartet of rare amber specimens, mined in the Hukawng Valley in northern Myanmar, is the earliest evidence of maternal care in fossilized spiders, reports CNN’s Ashley Strickland.
"Whereas we expected that spiders had maternal instincts from their very beginning, it is, nevertheless, very nice to have actual physical evidence from the fossil record about 100 million years ago," says study author Paul Selden, a University of Kansas geologist, to CNN.
After close examination, researchers from Capital Normal University in Beijing, China, and the Natural History Museum in London found that the spiders belonged to the now-extinct spider family, lagonomegopids, reports New Scientist’s Christa Lesté-Lasserre. Lagonomegopids first appeared during the Carboniferous period about 299 to 359 million years ago existed through the Cretaceous period, about 65 to 145 million years ago, per CNN. The spiders are known for their googly eyes at the corners of their head that closely resembles those of a modern-day jumping spider. The ancient spiders did not build webs; instead, they were free-living hunters that burrowed in tree trunks.
Each piece of amber tells the story of how these ancient spiders cared for their young. In one piece, a female spider was astonishingly preserved, clutching an egg sac filled with spiderling embryos nearly ready to hatch, according to New Scientist.
"The female holding onto an egg sac with little tiny spiderlings inside — that's exactly the position that you would find female spiders guarding their eggs," Selden tells Live Science's Laura Geggel. "So, it really is a typical female spider behavior caught in an instant by this fossilization process."
The remaining three amber specimens showed already hatched spiderlings near fragments of their mother's legs. Researchers counted a total of 24, 26, and 34 hatched babies in the each. The amber also had pieces of wood wrapped with silk strands, suggesting that these pieces were preserved remnants of a spider nest. Together, the findings indicate that the spider babies stayed nearby and were guarded by their mothers. As their nest flooded with resin, the mother chose to stay and protect her spiderlings, reports New Scientist.
"It's essentially being altruistic, I suppose, in biological terms, [when you're] doing something that could be a danger to you in order to protect your offspring," Selden tells New Scientist.
The four amber specimens are currently at the Key Laboratory of Insect Evolution and Environmental Changes at Capital Normal University, per Live Science.