Ancient web spins evolution story

By Helen Briggs
BBC News science reporter

The web is preserved in amber - ancient tree sap that has hardened like rock Enlarge Image

The oldest-known spider web with prey still entrapped has been found preserved in a chunk of amber in Spain.

The mesh of silk strands - snaring the remains of a fly, beetle, mite and wasp - dates back 110 million years to the time of the dinosaurs.

The fossil web appears to have been designed along the same lines as the round nets woven by modern spiders.

The find, described in Science, sheds light on the early evolution of spiders and the insects they fed on.

The web consists of some 26 silk strands preserved in a thin layer of amber together with an arachnid's prey.

Although it is not intact, enough of the web structure has survived to convince its discovers - from the University of Barcelona, Spain, and the American Museum of Natural History, New York, US - that it was probably a classical wheel-shaped, or orb, web.

Spiders have been fishing insects from the air for a very long time Dr David Grimaldi, American Museum of Natural History

It is possibly the oldest spider web on record; an earlier single strand of spider silk preserved in Lebanese amber has been discovered although it is unclear if this was part of a true web.

"The advanced structure of this fossilised web (from Spain), along with the type of prey that the web caught, indicates that spiders have been fishing insects from the air for a very long time," said Dr David Grimaldi of the American Museum of Natural History.

"Spiders today have a huge impact as predators on insect populations, along with birds and bats."

Flying insects

The find from the San Just site in Spain dates back to the Early Cretaceous, a time when Earth was home to the pterosaurs, the largest animals to fly, and many dinosaurs.

The web probably once looked like this. (Image: Science/Mark Chappell)

Winged insects were spreading rapidly across the globe. They were probably preyed on by primitive spiders, just as modern spiders that spin orb nets do today.

The 110-million-year-old spider web snared three of the four orders of flying insect, suggesting that the evolution of spiders and flying insects is inextricably linked.

"Biodiversity of spiders increases over geological time at a very similar rate to that of insects, which basically suggests that as insects are evolving, the spiders are evolving too," said fossil spider expert Dr David Penney of Manchester University, UK, who published details of a similar find last week.

Single origin

A second paper published in the current edition of Science also sheds light on the early evolution of spiders.

A parasitic wasp met its end in the web

Some have suggested that the orb web is an example of convergent evolution - when something evolves independently at different times in history, in this case twice.

But the new genetic study suggests all orb-web spinners share some key silk-making proteins, indicating a single evolutionary origin.

Coupled with fossil evidence, this suggests that the great ancestors of modern spiders were weaving webs as long ago as 136 million years ago.