Two short articles in this week's Science link the orb-weaving spiders back to a common ancestor in the Early Cretaceous, with both physical and molecular evidence. What we have is a 110-million-year-old piece of amber that preserves a piece of an orb web and some captured prey, and a new comparative study of spider silk proteins that ties together the two orb-weaving lineages, the Araneoidea and the Deinopoidea, and dates their last common ancestor to 136 million years ago.
Araneoids and Deinopoids build similar looking webs—a radial frame supporting a sticky spiral—but they differ in how they trap prey. Deinopoids spin dry fibers that they fluff into threads that adhere electrostatically to small insects; Araneoids secrete glue onto the the strand, which takes less work (no fluffing), and is much more strongly adhesive. The differences are enough to make one question whether there was a single origin of orb weavers, or whether the two groups independently stumbled on the same efficient form of architecture.
Continue reading "Old spiders" (on Pharyngula)