When walking through the woods or even in the backyard, people may run across a huge black and yellow spider, which may be weaving a large golden web or sitting waiting patiently for prey to get caught in the sticky threads. Spiders are in the Class Arachnida and are related to insects. In South Carolina, three big yellow and black spider species are the yellow garden spider, the golden silk orbweaver, and the joro spider, a relatively new species in SC. These large spiders are docile, are not generally considered dangerous, and provide a beneficial service by capturing and consuming other insects, some of which are pests of people, pets, and crops.
Yellow Garden Spider (Argiope aurantia)
The yellow garden spider is found throughout South Carolina. The body’s main color is a bright neon yellow with a splotch of black in the middle. The body is more spherical than other common yellow spiders, and its long legs are brown near the body but have prominent black tips on the end. Females are distinguished by these characteristics, while males are much smaller and more muted in color. Females can be up to 1 inch long, while males are rarely more than ¼ inch long. Garden spider webs are often found near open sunny areas, usually in tall vegetation (like a garden, hence the common name). The web is known for its intricate style, being circular but sporting a lightning bolt zig-zag pattern vertically through the middle of the web. This web decoration is known as a stabilimentum. Its purpose is still being debated – it may be to help attract prey or make the spider appear larger than it is (which would help the spider defend itself), or it may be to increase the visibility of the web so vertebrates do not walk or fly into it.
The round egg sac of the spider is usually shades of white or brown and can be found hanging on the web. When spiderlings hatch, they appear similar to adults in coloration. The only difference is their legs- instead of having brown and black legs, the juvenile spiders have legs that are orange and black. When the spiders mature, males will try to find a mate by spinning a web near or within a female’s web. To get her attention, the male will strum the web, alerting her of his presence. The pair will mate, and shortly after, the male will die, sometimes serving as a post-coital meal for the female. The female will then lay her eggs and encase them in an egg sac to protect them from the environment.
Spiders play an important role in the environment, and the yellow garden spider is no exception. They are harmless to humans but deadly to insects who become ensnared in their web. Occasionally, small vertebrates such as lizards may also become the spider’s meal. Once caught, the spider will encase the prey in its web for later consumption.
Golden Silk Orbweavers (Trichonephila clavipes)
Golden silk orbweavers are large spiders known for their expansive golden webs. Present around the world, these spiders are often found in areas with dense vegetation and a humid climate. The most common species in South Carolina is the golden silk spider (also called the golden silk orbweaver or banana spider), first documented in Charleston, South Carolina, in 1863.
There are many species of spiders that are considered orbweavers, and their colors can range from yellow to reds and greens. What makes them stand out as orbweavers is the trademark white cephalothorax (the body part with the head and where the legs attach), which the spider uses for heat regulation during hot days. These spiders have a hairy “bottlebrush” appearance on some of their leg segments. The size of these spiders is also impressive, with female bodies averaging between 1.5 and 2 inches long and males being a little less than 1 inch long. With their legs spread wide, these spiders can be as big as a person’s hand! However, what makes these spiders distinctive is their web: the silk spun by these spiders is made up of specific chemicals that make it golden in color. The reason for this color is still being studied, though it is thought that the yellow color can be attractive to insects or act as camouflage, as it can be difficult to see in the speckled sunlight of the forest. The web is also very intricate, and it is made up of both sticky and non-sticky portions. People have tried to use the web strands to make material for clothing, but due to its difficulty in acquiring, this has not been a successful endeavor.
Reproduction in this group is much less dangerous for males than it is in others. Males will seek out a potential mate carefully, preferably choosing a mate who is feeding. The male will alert the female that he is nearby by strumming the web, and if not met with aggression, will move forward in his advances. If the female shows any sign of aggression, the male will either wait for a different time to approach or flee. Once the male meets the female, the pair mate. Because of her immobility due to feeding (or molting), the male may successfully flee after mating without being eaten by the female. Although not as common in this group, some males are eaten after copulation. Multiple males will compete to mate with the same female, and those who mate with the female for a longer period of time have a better chance of producing offspring. The female will lay her egg sac within her web in an area with dense covering, such as under leaves. This provides the sac protection from predators. The eggs will hatch, and spiderlings emerge from the sac. Spiderlings look very different from adults. Rather than being bright like the adults, juvenile spiders are pale yellow with faint white and brown stripes on the abdomen.
Orbweavers can play either a beneficial or bothersome role, depending on how they are viewed. Their webs can be sticky and in the way of paths, though these webs are quite beneficial when it comes to ensnaring insect pests of fruits and vegetables. Regardless, orbweavers are not harmful to humans.
Joro Spider (Trichonephila clavata)
The joro spider has become a popular name in recent entomology news due to its recent appearance in the Georgia Piedmont and, more recently, South Carolina. It is common in Asian countries such as Japan, Korea, and China, and it even received its name from a Japanese entity known as the jorogumo, a spider demon. We do not yet know if there will be any negative impacts from this non-native species on the local ecology of South Carolina.
The joro spider is an orbweaver whose colors are vibrant and flashy. The arachnid has the distinctive white cephalothorax that orbweavers display, and its abdomen is bright yellow with gray or dark blue stripes and a red underside. Like other orbweavers, its web is also golden in color.
The Good News: Spiders and Their Benefits
Although spiders tend to have a bad reputation, they are quite helpful members of the ecosystems they inhabit. They serve as a natural form of pest control, preying on insects that may be harmful to crops. Although dangerous to small insects, the three spider species listed above are not harmful to humans. These species are quite docile, and if given the option, will run rather than attack. If by chance one does attack, the bite is similar to a bee sting and generally not dangerous to humans.