A Spider's Butt Resembling an Oreo Cookie

If you've ever found a small burrow in the ground with a trapdoor made of dirt, leaves, or other debris, and you're in the southeastern United States, though, particularly in Georgia, Alabama, and Tennessee, you may have stumbled upon the burrow of a ravine trapdoor spider.

 

This unusual looking spider can be easily identified by its flat butt that looks like an oreo cookie. Actually, it's the abdomen which is abruptly truncated and ending in a hardened disc. It uses this to clog the entrance of its burrow when threatened by predators, a phenomenon called phragmosis. 

 

When this part is sticking out of the ground, it also looks like an old dusty arcade token, or some kind of ancient coin. If you were to pick it up and pull it out of the ground, though, the rest of the spider would become visible. 

 

These medium sized spiders are generally dark brown or black, with thick, stocky bodies. They have robust fangs for chomping down on prey. 

 

Trapdoor ravine spiders (Scientific name: Cyclocosmia truncata) are generally shy and reclusive, spending most of their lives underground. Female ravine trapdoor spiders can live for many years, while males tend to die shortly after mating.

 

The purpose of the trapdoor burrows these spiders make is to provide both concealment and protection from predators and harsh environmental conditions. The burrow also makes it easier for them to catch prey. These spiders ambush predators. Rather than spinning a web to catch prey, they rely on their keen senses to detect vibrations from insects or other small creatures walking near their burrow. When they feel the right movement, they leap out quickly, grab the prey, and drag it into their burrow to eat.