|photo credit: mrspiderjoe|
Every year about this time, we get lots of calls from people asking about the large, showy spiderwebs they see in their yards and gardens. Almost always, the web-builder in question is the spinybacked orbweaving spider, Gasteracantha cancriformis.
Here’s where that Greek and Latin roots class comes in handy: the genus name means “stomach spine,” the species name means “crab-shaped.” At about ½” across when fully grown, it’s a rather small orbweaver, especially compared to the size of its web, which can be well over three feet across. The “signature” feature of a Gasteracantha web are the white tufts of silk – that from a distance look like white dashes – mostly placed along the outer support (foundation) lines of the web. These tufts don’t function in prey capture, but may give passing birds or other animals a head’s up that the web is there. The entire web is a beautiful work of art, especially when it reflects the oblique rays of the early morning or evening sun.
The spider too is quite pretty when you look close. The flattened abdomen’s upper surface appears coated with shiny enamel paint, and may be red, yellow, white, or black. Black or sometimes red spines radiate from the abdomen’s edge. Here’s a picture submitted by Troy of a beautiful red specimen (notice the tufts of silk).
Some people call them “crab spiders,” but true crab spiders do not build webs – they lie in wait for their prey in the center of flowers and are often pastel-colored. Coolest of all – some can change color over time to match their background, e.g., if they move to a different flower.
photo credit: Lyndi&Jason
Other orbweavers you may notice at this time of year are the garden spider, Argiope aurantia, and the banana spider or golden orbweaver, Nephila clavipes. Argiope webs are large and symmetrical, but instead of silk tufts, these spiders weave a thickened cross or zigzag (called a stabilimentum) across the center of the web. I am sure that Wilbur the Pig’s friend Charlotte was an Argiope – no doubt E.B. White got the idea of writing words in the web from seeing the stabilimentum.
In contrast, banana spiders build large, messy webs of extremely strong, golden silk. Often there are several individuals of different sizes in the golden orb webs. Banana spiders are very common in wooded areas south and west of Houston (e.g., Armand Bayou and Barker Cypress), and we usually have one or more on display in the Insect Wing.
Why do we see orbweaving spiders mostly in the fall? I suspect that they are around all summer, but both they and their webs are much smaller earlier in the season. By the way, most web-building spiders you notice are females; male orbweavers are much smaller. All three species mentioned above overwinter in the egg stage – the adults die at the end of the fall season, leaving only an egg sac behind.
Orbweaving spiders are completely harmless to humans and will not bite. Indeed, they are highly beneficial because they catch a variety of insects in their large webs. You can think of them as “green” and silent bug-zappers!
So – next time you see a big spider web, take a moment to look for the hardworking and talented spider that built it, and tell it (her) “hello, and thanks!”