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Giant lichen orbweaver (Araneus bicentenarius) adult female Report and Photographs Courtesy of Dawn S., Helotes, TX, 21 July 2007 Editor's Notes by Jerry Cates
Dawn Wrote: Jerry--I'm sorry that it took me so long to get back to you. I apparently sent the original e-mail via my husband's computer and he doesn't check his email as frequently as I do mine. We received over 4 inches of rain yesterday and I quite honestly didn't think that the spider would still be there today. But luckily we found her nestled in the leaves. I think we got a couple of shots of her underside but she was pretty curled up. Actually my husband, daughter and I were all taking shots of her the first night with 3 different cameras. We used a Nikon D70, an Olympus C-750 and the one that actually got the best shots was the Kodak Z612. My husband used the macro setting and forced the flash and at times we used a flashlight for lighting as well. Thanks--Dawn
Editor's Notes: This is a follow-up to a previous posting of the same spider. In the original posting, only the lateral and dorsal surfaces of the spider's body were shown. Here we can see the ventral body, and the underside of this spider is quite interesting. It sports a marking in the center of its ventral abdomen that looks like a yellowish "T" flanked by whitish splotches. Note that this marking bears no resemblance whatever to the markings on the ventral abdomens of the spiders we've seen from the genus Neoscona. In the latter spiders, the central mark is dark, and is surrounded by pale yellow or white markings, while here the central mark is pale yellow. The purpose for this marking (there doesn't have to be a purpose, but methinks there should be some practical value to it, inasmuch as a modicum of genetic investment is required to retain its shape and coloration) is open to conjecture, but one likely candidate seems particularly obvious.
Enlarging the above photo to reveal additional details of the ventral abdomen shows that the upper margin of the yellowish "T" lies just posterior to the epigynum (the darker semicircular structure just above the "T"). This is precisely where the male inserts his semen-laden pedipalp during mating. The male orbweaver must maneuver adroitly, as a single misstep places him at risk of being swathed in silk, killed, and consumed. Such does not forgive the slightest error, either in timing or, so to speak, targeting. Perchance the ventral marking assists the male in visually locating the female's epigynum, so that a pedipalp may be flawlessly inserted and its semen deposited, whereupon the male may make a safe exit without inciting the ire of his mate.
It is worthy of note that the structures on each side of the epigynum, which appear as lateral slits in the abdominal skin, are pulmonary spiracles that serve as respiratory orifices. Air drawn through these slits passes over a series of minute lamellae that resemble the pages in a book. Thus they form what is termed "book lungs". Book lungs are internal structures, and are not visible without dissecting the abdomen. However, their location can be inferred by the wrinkled, slightly darker (and in this specimen, reddish colored) region just anterior to the pulmonary spiracles. The exoskeleton in this region actually participates in the structure of the book lungs, inasmuch as the latter are invaginations of the former, and elaborated structurally so that they form the scaffolding for the lamellae through which the gaseous exchange of respiration occurs. Also worthy of note is the structure of the complex of spinnerets posterior to the marking we have been discussing. This complex consists of three pairs of spinnerets, an arrangement common to all spiders (except for certain Mesothelae, which have four pairs, and certain Orthognatha which have only two or, in a few species, merely one pair). The two anterior spinnerets are visible in the foreground of this photo, and the two posterior spinnerets are visible beyond them. A median pair of relatively diminutive spinnerets, positioned between the anterior and posterior pairs, is hidden from view (though in this photo a fan of silken fibers emanates from their spigots). Each spinneret is attached to an even more elaborate system of abdominal silk glands by ducts that end in multiple spigots on each spinneret. As many as six different kinds of silk glands are present in the spider's abdomen. The terminal regions of each spinneret are studded with spigots, each attached to a particular kind of silk gland, and each is capable of producing a separate silk line on command (the liquid silk solidifies on compression within the spigot, dependent strictly on internal tensioning). The musculature affiliated with each spinneret allows the spider considerable positional latitude as it spins multiple silk lines from each spinneret. As might be imagined, this latitude attains amazing complexity, rife with incredible flexibility for the spider. ----- Dawn, her husband, and her daughter, are ALL superb photographers, and are equipped with excellent, but quite different, digital cameras. Dawn mentioned that the best shots were taken with a Kodak Z612, a 6.1 megapixel camera with a 12:1 optical zoom, priced today (22 July 2007) below $300.00. The Nikon D70, another 6.1 megapixel digital camera, but with SLR capabilities and a multitude of optional lens, runs under $1,000, but significantly more than $300 (a refurbished, used model, can be had on the Internet for just under $700). The Olympus C-750 is a 4 megapixel digital camera with a 10x zoom, and a price tag around $430.00. This isn't the place to review digital cameras (though maybe it should be), but I am not surprised that the least expensive camera of the lot took the best photos. One reason the Kodak Z612 bested the Nikon D70 might have been the added complexity of the latter over the former. I often use a Canon EOS 10D SLR, with 6.3 megapixels, to photograph insects, spiders, and wildflowers in macro, and am sometimes disappointed in the results. That camera and its retinue of specialized lenses cost, not very long ago, in the neighborhood of $6,000, but it is regularly bested by cameras valued at less than $100. My old Sony Mavica FD91, for example, with only 0.8 megapixels, always produces excellent macros, though I have to carry a bunch of floppies to the field in order to make good use of it... Many thanks to Dawn S. for these excellent photos!!! ---------------------------------------------- Please contact us about your personal experiences, if you have been bitten by a brown recluse, black widow, 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. One 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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