By GEORGE VARGA

While out and about in Mission Trails, Rancho Mission Canyon, or in our backyard, we often see a fairly large spider in the middle of a large web consisting of concentric circles — an orb-weaver spider. The word “orb” comes from Middle English meaning “circle” and from the Latin “orbis” meaning “ring.”

Orb-weaver spiders are members of the family Araneidae (araneids) belonging to the class Arachnida that besides spiders includes scorpions, mites, and ticks. With more than 3,000 species worldwide, araneids are the third largest family of spiders.

The creation of the web is in many ways an amazing feat of engineering and construction. First, the spider rides on the wind, stringing a line to another surface. Once it has landed, it secures the line and then drops another line from the center of the first making a “Y.” It continues to add more radii starting from the center and then adds the concentric circles of webbing that gives the common name “orb-weaver”. The initial lines of the orb are spun with non-sticky silk, but the final spiral is of sticky silk which aids in the capture of prey.

Most orb-weavers tend to be active during the evening hours. Many of them will build a new web each day. They will consume the web toward the end of the day, rest for about an hour and then begin construction of the new one in roughly the same area as the original one.

Generally, when an insect blunders into the web, the spider will stun the prey with a quick bite and then wrap the insect with silk and consume it at leisure. If the prey, however, is venomous like a wasp, the wrapping may be performed first. Should you encounter an orb-weaver on your skin, keep in mind that they are reluctant to bite. However, if you do get bitten, the result is a mild local pain with some numbness and swelling. It is definitely not fatal.

Among orb-weavers, the difference between male and female, sexual dimorphism, is based on size. Males are always smaller than females. Orb-weavers also exhibit sexual cannibalism where the female will consume her male paramour.

In Mission Trails, a place that is sure to give you a chance to observe the web of orb-weavers is on the slope of Kwaay Paay right across from the entrance to the parking lot for Old Mission Dam. The best time to view is early in the morning after sunrise when the webs are outlined by dew.

— George Varga is a trial guide at Mission Trails Regional Park.