Spider webs spun from single origin

WASHINGTON -- The classic spider's web, like Charlotte would have woven, was invented just once, way back in the Cretaceous period some 136 million years ago, scientists report.

Two major types of spiders spin the orb web, and one explanation for its evolution was that the two groups forged the circular style independently of each other .

But a paper in today's issue of the journal Science says a comparison of the spider genes related to web-making shows that the orb web developed just once.

Researchers led by Jessica Garb of the University of California, Riverside, compared spiders that built orb webs in the genera Deinopoidea and Araneoidea. Garb said in a statement that the finding ``does not support a double origin for the orb web," but indicates that the unique design evolved only once .

While the two groups probably developed orb-web spinning from a common ancestor, they came up with different ways of making the web catch prey. Araneoid webs have glue droplets that make prey stick , while deinopoids wrap their threads with a of silk fiber that ``the spiders comb, until it almost has the appearance of Velcro under a microscope ," Garb reported.

In a separate paper in the same issue, a team of researchers reports the discovery of a Cretaceous-era spider web encased in amber along with some captured insects. The amber, found in Spain, preserved 26 strands of silk, many of them connected to one another. Glue droplets are visible on the web and prey includes a fly, a mite, a beetle, and a wasp.

The amber was dated to about 110 million years ago and is the oldest known example of a web with trapped insects, said David A. Grimaldi of the American Museum of Natural History. This finding confirms that spiders and complex, sticky webs date back early enough to have affected the evolution of the most diverse groups of flying insects, the researchers said.