Yellow garden spider (Argiope aurantia) mature female
College Station, Texas 2006

Photography by Lorraine E.

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.