Sounding like a curse out of the Harry Potter movies, the word "stabilmentum" refers to a zigzag-shaped line of spider webbing that orb weaver spiders add to their webs. There are unconfirmed theories as to its function ... to attract insects, to help camouflage the nearby waiting spider, or to create a visual barrier so that birds do not fly through the web. The only thing we know for sure is that the stabilmentum superficially resembles writing, or letters of the English alphabet, and thus the common name of "writing spiders" is given to the orb spiders.
Here you see a female Black and Yellow Garden Spider (Argiope aurantia)... one of the most common orb spiders found in North and Central America. Common in milkweed patches and wetland areas on the UC-Hopland Research & Extension Center, these spiders tend to be local staying in one place throughout their lifetime. The web is a distinctive circular shape up to 2 feet in diameter, with the dense zigzag-shaped stabilmentum in the Center. The spider is usually found up-side-down near this centerpiece awaiting its prey to become ensnared in the web.
A nightly ritual occurs where the spider consumes the circular interior part of the web and then rebuilds it each morning with fresh new silk. The spider may be recycling the chemicals used in web-building, but this has not been proven. These spiders are not harmful to humans.
