Sticky Subjects: Insights into Ancient Spider Diet, Kinship
Perkins, S., Science News
Remnants of a spider web embedded in ancient amber suggest that some spiders' diets haven't changed much in millions of years. Separate research indicates that some groups of modern spiders that spin webs in the same pattern didn't stumble upon that design independently, as scientists had suspected, but evolved from a common ancestor. Both studies provide glimpses of spiders' evolutionary history.
Spider silk is made of proteins, so it degrades quickly and rarely fossilizes. When old specimens are found, they're most often preserved as single strands in amber, says David A. Grimaldi, an entomologist at the American Museum of Natural History in New York City. But in a piece of 110-million-year-old Spanish amber, he and his colleagues discovered a collection of silk strands. They describe this oldest known example of a multi-strand web, which still contained several insects, in the June 23 Science.
Grimaldi, his museum colleague Enrique Penalver, and Xavier Delclos from the University of Barcelona found pieces of at least 26 strands of silk preserved in the amber fragment, which measured about 18 millimeters in length. The longest strand of silk is about 5.7 mm long, and the strands generally measure between 0.6 and 1.9 micrometers in diameter.
Most of the silk strands are straight or slightly curved, and some are connected in a pattern similar to that seen in webs spun by modern orb-web spiders. In such webs, long strands of silk connect at the center, like spokes of a wheel, and the sticky threads that capture prey spiral out from that center.
Small droplets, presumably of spider-produced glue used to make the web sticky, adorn two of the strands preserved in amber, another sign that the ancient web maker probably was an orb weaver, says Grimaldi. …