Arabesque Orbweaver (Neoscona arabesca)

Report and Photograph Courtesy of Kathleen W., Houston, Texas, June 3, 2007

Kathleen Wrote:

Jerry--I have a bunch of photos of this spider to send you.  Some are a little blurry, but I couldn't bear to delete them.  Let me know which one(s) you like!   I'll be sending 10 photos in all, probably in a few batches.  I took these last night, the 2nd of June, at about 11pm, in the West Memorial area of Houston-- Kathleen

My Reply:

Kathleen---Beautiful photos!  This is, methinks, the arabesque orbweaver (Neoscona arabesca), one species in a genus that contains what we might call "workhorse" orbweavers--the ones that are not quite as showy as, say, the yellow garden spider (Argiope aurantia), but that are so numerous in our croplands and forests that the work they do in killing pesky flying insects makes them unusually valuable.  Some authorities have estimated that in certain locales these and similar spiders are present in numbers of up to 2,000,000 spiders per acre.  That's about 43 spiders per square foot.  Obviously, that could only happen in three dimensional space, with considerable vertical habitat.

Notice the markings on the dorsal abdomen in the above photo.  The arabesque orbweaver has generally three pairs of  dark markings that form "commas" whose thickest portions are near the midline; the commas then stretch laterally outward, pointing slightly forward toward the head.  At the median anterior dorsum of  the abdomen are four spots that form a trapezoid, with a pale border on each lateral margin.

Underneath this orbweaver's abdomen is a square-shaped marking outlined on the sides and at its anterior margin in pale yellow, with a dark center that extends to the entire posterior edge and the central fourth of the anterior edge, that is shaped like a vase--with a narrow anterior neck, a broad center, and a broad posterior base. This  square marking, in its generalized format, is probably present with most spiders in the genus Neoscona, but the shape of the dark central mark varies from one species to another.

Some authorities indicate that the same marking is also present in members of the genus Araneus, though it is clearly not present in the giant lichen orbweaver (Araneus bicentenarius), and that the only gross anatomical distinction between the genre Neoscona and Araneus is the presence, on the posterior carapace, of a transverse thoracic groove in the genus Araneus vs. a longitudinal groove in the genus Neoscona. Unfortunately, the structure of the thoracic groove is often obscured by the abdomen or by the hairs of the carapace.  In Kathleen's photos, only the photo below shows the portion of the carapace where the thoracic groove lies. Inasmuch as this photo is slightly out of focus, the architecture of the groove is in doubt.

The eight eyes of spiders in the genus Neoscona are almost equal in size, and form an ellipse that is flattened vertically and stretched horizontally.  Four eyes are in the center of the face, with two on top, and two on bottom.  The two largest (the posterior median eyes, or PME) are on top, and are closer together than the two below them (the anterior median eyes, or AME).  On each lateral face are two smaller eyes, the upper of which is designated the posterior lateral eye (PLE), while the lower is the anterior lateral eye (ALE).