Orb Weaver Spiders
We all have those moments in our lives that we will never forget. My encounter, as a young boy, with a large garden spider at the home where I grew up is one of those moments, branded in my brain in living color. While walking on a pathway with large shrubs on either side I felt the unmistakable encounter with a spider web, draped across my face and upper arms. So, I immediately stopped and began removing the webbing from my skin, wondering where the owner of that webbing might be. A glance at my shoulder solved the mystery, as the Orb Weaver spider was sitting right there, probably wondering just who the heck I was to ruin its web like that. Without exaggeration, I must have jumped three feet straight up into the air, while simultaneously and quite violently knocking the spider off of me. I apologize to spider-lovers everywhere, but the surprise of the moment took control of me.
Orb weavers really are some of the most fascinating spiders in our gardens, the architects of those lovely webs of perfect symmetry and design. They often are referred to simply as Garden Spiders, or perhaps by the Latin name of the genus of many kinds, called Argiope spiders. With several thousand species found worldwide and nearly 200 different kinds in North America, at some point in time you are bound to come across them. They seem to become more common and noticeable in the late summer and fall, as all of the eggs produced by the females have hatched, and the new spiders have set about their task of creating webs and catching their food. Rather than racing around on the ground, hunting for their food in the manner of wolf spiders or jumping spiders, orb weavers are a "lay-in-wait" predator, preferring to let the food come to them. Their webs are built in conspicuous locations, often across gaps that might serve as flight paths for insects such as moths or flies, and the sticky strands of the orb weaver's web do a marvelous job of capturing these other bugs.
The silk used for web making is produced by the spider, spun from glands located at the tip of the abdomen. The chemicals used for making this silk are a precious commodity for the spider, and it is not to be wasted. If a web has gotten a bit tattered, perhaps from too many insects being caught or from a small bird blundering through it, the spider will dismantle the web, dissolve and consume the silk, and recycle it to form new silk for a new web. It is not unheard of for some species to create new webs, or large parts of them, every night. The spider itself overcomes the problem of sticking to its own web by using specialized claws to climb around, and an oily substance on its claws to allow it to move along. Some webs may simply be a combination of sticky threads and non-sticky threads, and the spider knows how to move from place to place using the threads that it does not stick to. The insect prey, however, are not so well adapted, and a slight touch on the web may cause it to be stuck. As the insect bounces around, desperately trying to free itself, the orb weaver detects the movement of the webbing, and immediately rushes over to bite the insect, paralyzing it so that its frenzied movements stop, and then wraps that bug in silk for later consumption.
The bite of orb weaver spiders is not considered dangerous to people. As all spiders do, orb weavers have venom in their bite, and this normally is used only for subduing their bouncing prey. However, the spider also will defend itself, and if we were to handle the spider by squeezing it or pressing on it the spider may try to bite in defense. It is impossible to anticipate the effect on people who are highly sensitive to insect venoms, but for most people the bite should result in only local pain, reddening and swelling, and an effect similar to a bee sting which should go away fairly quickly. If you are concerned though, you should consult with your doctor if you are bitten by any spider. In North America it is the Black Widow which has the most dangerous venom, and the only one capable of actually killing a human. The bites from other legendary spiders, such as the Violin Spider or Hobo Spider, may cause a lingering sore on the skin at the site of the bite, but properly cared for this wound should disappear and cause no serious effects for most people.
As you observe an Orb Weaver resting on its web you may notice that it often rests right on the center of that geometric pattern. There often will be thickened strands at that point, with the spider's legs positioned over those thicker areas, perhaps to help it blend in and be less noticeable. There is also the suggestion that those thickened strands of the web help to make the web more noticeable to birds, which could destroy the web if they flew through it. A third hypothesis is that the thickened strands, referred to as the "stabilimentum", could be a lure to insects to help draw them to the web.
Another interesting observation you might make when watching an orb weaver, is that if you lightly blow on it or touch it with a strand of grass, it immediately begins bouncing up and down on its web. Obviously this movement is designed for some benefit to the spider, but exactly what that is seems difficult to discover. Perhaps it causes alarm in a potential predator, perhaps it is a defensive movement that would keep a predator from easily grabbing the spider, or possibly it helps move the web itself so that a potential prey is more readily caught in the silk. As big as they are, orb weavers are not without their own enemies. In the tropical jungles of South and Central America there are amazing damselflies, with abdomens 4 to 6 inches long, that prey on orb weavers. The damselfly is a close relative of dragonflies, but with much narrower wings and a very long, thin abdomen. These beautiful insects hover in front of the orb weaver web much like a helicopter, and then dart in to capture the spider when an opening is seen. The bouncing of the spider may make this capture more difficult. The Orb Weavers employ another defense against these enemies of theirs, by creating a second line of webbing just outside their capture webs. As their predator brushes against this outer web it alerts the orb weaver to the potential danger, and it has the option of scurrying off to hide.
Some of the common Orb Weaver species in the United States are extremely large and colorful, with shimmering silver or gold patches on the back of their abdomen. These are members of that genus Argiope, and fittingly may be named the Silver Argiope and the Black and Yellow Argiope. These are the ones we so often see out in our gardens, and if we can overcome our Arachniphobia a bit we truly can appreciate their beauty and benefit. Another group of orb weavers, in the genus Araneus, are a bit more gruesome looking. They do not have the showy colors of the Argiope species, and they have enormous, bulbous abdomens. These may be more likely to place their webs against your home or in the arbor over your patio. I once found a large web suspended between a support post and a rafter on my own patio cover, and took a stick and removed the web. The next morning the web was back, perfectly formed and ready to go. One of the methods for controlling spiders non-chemically is the suggestion that you simply remove the web. Obviously this may not work for orb weavers, which can rebuild that web rapidly overnight.
Another interesting group of orb weavers are the Spiny-backed Spiders in the genus Gasteracantha. These smallish spiders look for all the world like little crabs, with spines sticking out to the sides of their abdomen, which may be colored white with red spines or simply brownish. One species is called the Asian Spiny Back Spider, and while it is native to the oriental regions of eastern Asia it now can be found throughout the world in tropical regions. It began showing up in Hawaii in 1985, and now is found on nearly all the Hawaiian islands, becoming a serious problem there. It potentially can bite, and agricultural workers encounter them commonly in fields. The huge numbers of these spiders, with their webs placed nearly everywhere between branches and trees, may cause a problem for native insects on the islands, whose populations could decline because of the predation by the spider.
So, hopefully the next time you encounter one of the colorful orb weavers in your garden you will take just a few minutes to stand and observe it rather than killing it. It should not be our goal to create a garden with no bugs in it, and while we tolerate and welcome predators such as ladybugs and lacewings, somehow we have been instilled with a fear of all things spider. Their benefits, though, greatly outweigh their dangers. If you should decide that elimination of the spiders around your home is in your best interest, a thorough job may require the use of insecticides, and a licensed professional has excellent products for this use. The professional also has the training and education to identify the spider correctly and determine what impact it could have on you. He also has materials available for removing webs, as well as chemicals that can be applied to surfaces on your home to discourage the web-making of spiders.