99 million years ago the spiders were guarding their egg sacs and possibly caring for already hatched spiderlings when they were trapped in sticky tree resin. The now extinct female of the Lagonomegopidae spider family protects the egg sac with a hollow tree.
The hardened resins trapped arachnid moms in four masses of amber. The chunks of amber recently mined in Myanmar are now considered the oldest evidence of maternal care in spiders.
Of the four amber chunks, the most extraordinary is a piece holding a large female spider with part of an egg sac under her. This spider’s facial appendages, spineless legs and trichobothria, or “sensing hairs,” indicate that she is a member of the Lagonomegopidae family, a now-extinct group of spiders that lived in the Northern Hemisphere during the Cretaceous period (145 million to 66 million years ago). The mother’s protective stance over her egg sac is suggestive of maternal care.
The amber even preserved the silk thread that wrapped the spider’s eggs together. Some scientists think that spiders originally used silk to bundle their eggs together, and then later used it for other purposes, such as webs. The other three specimens hold spiderlings one with 24, another with 26 and a third with 34 hatchlings.
One of the amber specimens with hatchlings contains spider silk entwining pieces of detritus, which may have been part of a nest that the mother built to guard her egg sac. This suggests that the hatchlings stayed with their mom in the nest after hatching, rather than immediately dispersing.
The four amber specimens are now housed at the Key Laboratory of Insect Evolution and Environmental Changes, at the College of Life Sciences at Capital Normal University in Beijing, China, where study co-researcher Dong Ren is a curator.