GOAL: To learn about the history of spiders and their silk. Specifically, this activity highlights the fact that spiders have been around and using silk before insects took to the air.
BACKGROUND: Spiders and their relatives are among the earliest animals known from the fossil record. Attercopus fimbriunguis is a 380 million year old (Devonian) fossil that was originally believed to be a spider. Although scientists contend that Attercopus produced silk, it is not considered a spider because it did not have spinnerets; it may have been the ancestor of today’s spiders or at least a close common ancestor. The oldest fossil of a living spider group belongs to Mesothelae and is 290 million years old (Permian).
Living Mesothelae dig burrows in moist soil and line their burrows with silk. They then build a trapdoor using soil protein to glue various materials together. They hide in the burrows, which offer protection from predators and prey. Their trapdoor also creates a membrane between underground and above-ground air which moderates humidity and even protects from short-term flooding.
Mesothelae are entirely nocturnal. Some keep at least one foot in their door, waiting to sense and capture prey. Others use silk to extend their hunting ground beyond their doorstep. They lay down 6 – 8 ‘trip lines’ that radiate a few centimeters from their door. These lines are slightly raised and passing prey “trip” on these lines, sending a vibration back to the spider so that it knows when and where to pounce. Mesothelae also use silk for egg protection.