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Yellow garden spider
(Argiope
aurantia) mature female Photography by Lorraine E., text by Jerry Cates
The female of this species rests in the middle of its orb web, face downward, usually (as with this specimen) on a surface of the web covered by specialized silk known as the stabilimentum. This web appears to have about 32 radial threads. A close examination suggests that the spiral threads immediately surrounding the hub where the spider is resting differ in reflectivity from those further out on the web. The spirals near the hub are free spirals of the same structure as the radials, and are not intended for catching prey, while the outlying (catching) spirals are coated with droplets of glue-like material. This species dismantles its web every night, rebuilding it in 30-40 minutes. Each new web remains in place throughout the day, with the female positioned in the center of the hub most of the time.
The head of this species is flattened frontally, with all eight eyes facing forward. The two posterior median eyes (PME) are visible in the photo below as two eyes in the middle of the upper face. A protuberance, directly below the PME, encases the two anterior median eyes (AME). Lateral protuberances on each side of the face each house two eyes, one the posterior lateral eye (PLE), the other the anterior lateral eye (ALE).
Fortunately, the extreme resolution of Lorraine's photographs, and her steady hand, enable enlargements that show considerable detail. The silvery hairs that cover the carapace, above, cannot obscure the cephalic groove that marks the fusion of the head to the thorax. Note the coloration of the front legs. In Argiope aurantia, the coxae (where the legs attach to the thorax) and femurs (the first long segment of the leg) of leg 1 are dark in color in the mature female, but yellowish orange for legs 2-4. Note also the numerous hairs, or bristles, on the legs. These are highly functional sensilla (see Rainer F. Foelix, "Biology of Spiders", 2nd Ed., chap. 2, functional anatomy) found on all leg segments. Those on the proximal segments (e.g., the coxae and femurs, as in the photo above) are mostly mechanoreceptors for touch and vibration. Those on the distal segments (e.g., metatarsi and tarsi, shown below) tend to be more complicated, and include chemosensitive hairs that let the spider test the chemistry of objects in contact with their leg tips.
Many thanks to Lorraine E. for this excellent photograph. ---------------------------------------------- We are investigating the risk of secondary infections that may occur as a result of bites from this and other, otherwise harmless spiders whose venom is known to pose little or no danger to humans. In the process, we are collecting information on experiences persons have had with such spider bites. Please contact us about your personal experiences, if you have been bitten by this or any other spider, including jumping spiders and garden spiders (the bites of which typically produce a transitory inflammation, but resolve within a few days without medical attention), whether recently or in the past thirty years, anywhere in the world. For example, the bite of a species of garden spider, the golden orb spider of Australia [Nephila edulis] typically is unremarkable, but on occasion produces medically significant secondary infections; the frequency and nature of bites experienced from that species of spider is also a part of this study. The object of this study is to collect data that might relate to a mysterious series of spider-related infections, involving a special pathogen, that took place in the United States and in Australia between 1977 and 2006. Although only fifteen such infections were reported to medical establishments, seven appear to be associated with spider bites. Some authorities suggest that the number of actual infections of this type that occurred in the U.S. and Australia during the past thirty years is much larger, but that they have been underreported. Underreporting of specific kinds of infections can occur, either because the persons infected chose not to seek medical assistance, or the medical establishments misdiagnosed the infections as being caused by other infectious agents. We are seeking to establish an estimate of the number of human spider bites that occur each year by these and similar spiders, whether the bite resulted in injury to the human or not. Next, we hope to establish the number of instances where the bite (1) became inflamed and/or infected, then resolved without medical intervention, or (2) infected, ulcerated, or led to a generalized sickness, and required medical intervention. ---------------------------------------------- Back to: Texas Spiders Back to: Bugsinthenews |
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