Western Spotted Orbweaver (Neoscona oaxacensis)

Photographs Taken in Dripping Springs, Texas, 6 June 2007

These spiders are present in large numbers in the superstructure over a private water treatment plant in the little Hill Country town of Dripping Springs.  They are quite large, due to the quantity of prey that their webs capture each day.  As the photo below shows, many of their webs are built on a horizontal plane, which is not typical for the species.  However, prevailing winds are downward at this site, due to the action of the water treatment machinery, and that makes a web on the horizontal plane more useful than one on the vertical.

The female has a large, globular abdomen and diminutive pedipalps (the short appendages in front of the spider's mouth, which are easily seen in the photo below). The markings on the dorsal abdomen, shown in side view above, and in dorsal view immediately below, are ornate and complex. These markings are definitive for Neoscona oaxacensis. 

This spider has eight eyes, arranged in an elliptical pattern, shortened vertically and stretched horizontally, with the two largest eyes in the middle of the upper face.  Those eyes can be seen in the photo below as small black spots.  Note that the cephalic groove delineating where the head is fused with the thorax, is easily seen, and forms a "V" behind the head.  This "V" meets the thoracic groove (that separates, in this genus, the thorax into right and left halves) to form, in combination, a "Y".  This anatomical feature distinguishes the genus Neoscona from its sister genus Araneus.

Notice the structure of the legs in the above photograph. The coxae are not visible, being hidden by the carapace, so the first proximal segment (the longest and thickest leg segment) is the femur. The femur is attached to the next-longest segment the tibia, by a short, stout patella. Take note of the dark spots on each patella, particularly the lateral spots, distally and proximally.  These are likely sensilla of some kind.  The relatively thick tibiae of legs 1 and 2 connect to remarkably slender metatarsi (only a mite less remarkably for legs 3 and 4), and thence to tarsi of comparable girth, which are less than one third the diameter of the tibiae. These distal segments (metatarsi and tarsi) contain most of the sensory organs of the spider's ambulatory extremities.

The photo below is of the female's ventral body.  The sternum (ventral carapace) is usually white, ringed with darker coxae (the attachments for each leg).  In the center of the ventral abdomen is a square-shaped set of markings common to most species in the genus Neoscona.  The square appears, in this species, as a black cross, with a staff and crossmember, the lower portion of the staff being broader than its upper portion. The cross divides the square into four sections, each of which, except for the black cross itself, is white.

Anterior to this mark are the lateral respiratory spiracles, seen as slits in the spider's skin (along the anterior edge of the marking) that serve as orifices leading to the right and left book lungs.  The reddish, smooth area anterior to the slits are hardened cuticle covering the book lungs, from which the book lungs are formed.  Midway between the two respiratory spiracles lies the epigynum; in the photo below we see what appears to be a sclerotized structure just posterior to the median. As shown in the enlargement of this area, pictured below, the scape is deltoid in shape, which is consistent with Ubick et al. (2005), pg. 74, dwg. 17.67-8.

Posterior to this mark is an orange-colored square enclosing the spider's complex of spinnerets.

Photos of the male western spotted orbweaver...