‘Spider mom’ from 99 million years ago found beautifully preserved with egg sac in amber

BEIJING — A prehistoric cannibal spider that scurried around the feet of dinosaurs was captured forever in Burmese amber. This “spider mom” is one of the world’s first recorded cases of maternal care in the animal kingdom. Frozen in time by sticky tree resin, scientists are able to observe her and her babies, shedding fresh light on evolution. 

The extraordinary fossils from Myanmar date back 99 million years to when T-Rex ruled the Earth. Scientists say she was guarding spiderlings and egg sacs – pear-shaped silky bags loosely woven on the silk. She would have carried the sac in her jaws or spinnerets and looked after the baby spiders, or spiderlings after they hatched.

“Maternal care can enhance the survival rate of offspring. It represents a breakthrough in the adaptation of animals to their environment – and has significant implications for sociality,” the authors write in the study, 

Photographs and drawings of a lagonomegopid spider and egg sac in Burmese amber.

The ancient arachnid belonged to the extinct Lagonomegopids. It was less than half an inch long, with hairy legs and bulging eyes. “Adult female lagonomegopid spiders probably built and then guarded egg sacs in their retreats or nests. The hatched spiderlings may have stayed together with their mother for some time,” the authors explain.

“Lagonomegopid spiders were active hunters rather than web weavers. They preyed on insects such as flies and beetles, or even other spiders. And they might have been preyed upon by insects, early birds, small dinosaurs, and even other spiders,” says lead author Dr. Xiangbo Guo, a life scientist of Capital Normal University in Beijing, in an interview per South West News Service.

Myanmar has yielded a treasure trove of discoveries of skin, scales, fur, and even feathered tails of dinosaurs. Some specimens are a couple hundred million years old, and have been invaluable to finding out about the story of life on Earth. Since amber has a unique ability to entomb ancient plants and animals in its transparent resin, it opens a window into the past. 

Ecological reconstruction of a female lagonomegopid spider guarding her egg sac. Painted by Xiaoran Zuo.

The species lived in moss at the bottom of tree trunks. Although it was capable of producing silk using its spinnerets, it was unlikely to have woven webs. The creature’s remote habitat and small size make it a possibility that descendants could still be living in the forests. 

 

Spiders have been around for 400 million years, making them one of the success stories of the natural world. They have evolved several unique features, including spinnerets and venom for immobilizing prey. There are more than 47,000 living species today.

“Maternal care, all aspects of the mother’s caretaking activity, has diverse forms across the animal kingdom. The new fossils represent early evidence of maternal care in fossil spiders, and enhance our understanding of the evolution of this behavior,” the authors write.

The study is published in the journal Proceedings of the Royal Society B: Biological Sciences.

South West News Service writer Mark Waghorn contributed to this report.