This spider’s eyes glow, even though it died 110 million years ago

Fossil hunters in Korea discovered long-dead spiders preserved in rock. And to the delight of scientists, the arachnids’ eyes are still reflective — some 110 million years after the creatures died. 

It’s rare for insects — which are far more brittle than shelled sea creatures — to become fossilized in rocks. But for reasons still unknown, a couple of these spiders did fossilize, and the unique shape of their eye structures continue to reflect light — even in their petrified form. 

The reflective eye structure is called a tapetum, and it’s often used by creatures who hunt in the dark. 

“So, night-hunting predators tend to use this different kind of eye,” Paul Selden, director of the Paleontological Institute at Kansas University’s Biodiversity Institute and Natural History Museum, said in a statement. “This was the first time a tapetum had been in found a fossil. This tapetum was canoe-shaped — it looks a bit like a Canadian canoe.”

A 100-year-old spider with reflective eyes.

Today’s wolf spiders employ the same eye structures to hunt, Selden added.

A mystery still remains, however: How did the spiders become fossilized? Their petrified bodies were found in a layer of rock filled with fish and other sea critters — but spiders don’t dwell in water.

“It has to be a very special situation where they were washed into a body of water,” Selden said. “Normally, they’d float. But here, they sunk, and that kept them away from decaying bacteria — it may have been a low-oxygen condition.”

Another view of the fossilized spider.

Selden and his Korean colleagues — who actually discovered the ancient spiders — now get to name the curious fossils. They were only found because Korean land is often excavated, so scientists and the fossil-curious dig in to see what ancient novelties are hidden in Earth’s crust. 

“So, they carve away the hillsides to make a flat area, and there are temporary excavations while they’re cutting away and building a factory or whatever — that’s where they found these fossils,” said Selden.