A Mature Female Southern Orb Weaver in Houston, Texas

This article by Jerry Cates and Andrea G., first published on 29 March 2010, was last revised on 24 April 2016. © Bugsinthenews Vol. 11:03(22).

—————————————–

Southern Orbweaver Eriophora ravilla 032710 Andrea G

Southern Orbweaver (Eriophora ravilla) 03.27.10 Andrea G., Ventral Body & Legs

Andrea wrote:

Hi,  I took this photo in my yard on Saturday night – 3/27/2010. I think I got the “wrong” side of the spider, from what people have said, as it does not seem to be the side that has identifying marks.

The leg-span of the spider is several inches. The web was in my garden, near the side of my house, which is why I could not get on the other side to get a photo from that angle.

I’ve been trying to find photos online that would help me identify this, and came across your site so thought I’d ask. If you know a name, that’s great – I can research from there.

Thanks so much for even taking time to consider emails from the spider-ID-challenged like myself!    Andrea G.”

I thanked Andrea for her excellent photograph, then hastened to explain that although most folks suppose the markings on the back of the spider are the most telling, the marks on the underside are even more important. Her photograph was perfect for identifying this specimen, immediately, as a Southern Orbweaver.

The generic name, Eriophora, is from the Greek erio = “wool”, and phorein = “to carry”, and thus means, “one who carries wool “, or, as discussed in Ubick, et al. (2005), p. 293, “wool bearer“. Eugène Simon (April 30, 1848 – November 17, 1924) was the French arachnologist who, in 1864, first named a “groupe” of spiders under this designation, using it to refer to their orb webs. His many taxonomic contributions include categorizing and naming many spiders, as well as creating genera such as Anelosimus, Psellocoptus and Phlogius. He did not elevate Eriophora to the status of genus, however. That was left to Frederick Octavius Pickard-Cambridge (November 3, 1860 – February 9, 1905), an English arachnologist, who did so in 1903.

The genus Eriophora comprises 22 species worldwide; two (E. ravilla and E. edax) are native to North America. Eriophora ravilla is probably quite common in the southern U.S. Many photographs of this species were sent to me in 2009.

Andrea’s photograph, above, has been reoriented, sidewise, head left, posterior abdomen right. This orientation is easier to view on most computer screens. The original orientation of the image has the spider with its head down, in the normal manner of typical, resting orbweavers.

It was also somewhat exciting to look at, as one of the anatomical features of this spider is of particular interest, but is more often than not missing in specimens photographed in the field.

Southern Orbweaver (Eriophora ravilla), ventral abdomen 032710 Andrea G.

Southern Orbweaver (Eriophora ravilla); ventral abdomen, 03.27.10 Andrea G.

Bear with me, as I digress for a moment t0 point out some landmarks to help explain what follows:

The Spinnerets: Notice the enlargement of the ventral (underneath) abdomen, on the left. Do you see where the hairy underside of the abdomen becomes smooth, lacking hairs, at the posterior end (the uppermost portion in this photo, as the spider is standing on its head)? The structure you see here is that of the spinnerets, which are six in number. Two, in foreground, are rather easy to see, and two additional ones, back of these, can be inferred as present though they are not easy to pull out of the image. Two additional spinnerets, which are smaller, are obscured in the middle and not visible.

The book lungs: Now do you see the bright reddish areas near the legs, in the lower third of the abdomen? These mark the hardened, sclerotized tissue that covers the spider’s pair of book lungs and gives these lungs the support needed to maintain their structural integrity.

The Epigynum: Now, finally, notice between those two reddish areas a shiny, brownish-red structure, that is aligned with the long axis of the spider’s body. The posterior end (the upper portion) of this structure is darkened, and has a needle-like extension that projects back, toward the spinnerets. This is the scape of the epigynum. In most orbweavers the architecture of the scape is definitive for each species, and that is very much the case in this species, as female spiders in the genus Eriophora have unusually long scapes that extend more than halfway to the spinnerets. As you can see, this scape does just that.

Most of the specimens, of this species, that  I see in the field have scapes that are much shorter. Methinks they have lost their original scapes, probably during mating.  This specimen has lost a leg (leg III on the left side, in the dorsal perspective) which suggests some kind of trauma has been experienced in the past, but somehow the scape has been retained.

Andrea may be able to take additional photos. Stand by for–hopefully–additional material on this beautiful spider.

The Southern Orbweaver, as with most of our native North American orbweavers, is not considered a dangerous spider. It will bite if handled, or if accidentally trapped between the web and one’s body, but the bite is not considered medically important.

—————————————–

Questions? Corrections? Comments? BUG ME RIGHT NOW! Feel free to e-mail jerry.cates@entomobiotics.com. You may also leave a comment in the space provided below.

Leave a Reply

  

  

  

%d bloggers like this: