Yellow garden spider (Argiope aurantia), Justin, Texas
Report and Photographs Courtesy of Stephen M, 28 July 2007
Jerry--I went out today to get photos of the underside of the banded garden spider, but she was not out where I could see her. I did get several pictures of her babies and attached one for you. While there I noticed, about 20 feet away in a tree, a huge yellow garden spider. You already have several others posted of this species, but I got great shots of the underside and frontal and direct for the eyes. If you wish, I'll send them on. I am looking for other types to send you as well---Steve [Editor's Note: Justin, Texas, is between Fort Worth and Denton, just west of Interstate 35W] .
Editor's Notes: The yellow garden spider (Argiope aurantia) is one of our most photogenic spiders, and although I have not counted, no doubt more photos of this species are posted on this website than of any other. Some may question, for that reason, why I so readily post new photos of the same species as they come my way. The answer becomes clear by looking at these photos and noting the additional features they show that are not so well defined in the photos that came before (and, conversely, the features shown in those earlier photos that aren't displayed here).
Every new set of photos reveals more information. Furthermore, each new specimen shows subtle differences between one specimen and another in, for example, marking arrangements. To those of you with these spiders in your yard or garden, I urge you--send in some photos. They will probably show us things we haven't noticed before, and will be worthwhile additions to our existing array of photos. It is a rare day when new photos of even a common spider do not show us something we had not observed in previous photographs.
A distinctive anatomical feature of spiders in the genus Argiope is the positioning of their anterior median eyes (the AME, or the two eyes lowest on the head, in the middle of the face). For these spiders, the AME are closer together than they are to the lateral eyes. In the above photo we can see the two posterior median eyes (PME) in the foreground, surrounded by dark margins and the whitish gray hairs of the carapace. Directly below them, a prominence with dark margins projects outward from the head and contains the anterior median eyes (AME). Though we cannot make out the eyes in this structure, it is obvious that they are close together, and that they are a considerable distance from the darkened areas on the periphery of the face, midway between the PME and AME, where the lateral eyes are positioned.
The orange-colored structures emanating from each side of the face, stretching outward, then down, are pedipalps, leg-like appendages without metatarsi that are used, not for locomotion but--in the female--for catching and manipulating prey.
Steve took an excellent photo of the head (enlarged from the above photo and shown below), showing the prominences holding both the AME and lateral eyes. Although the actual eyes are not shown, their positions are obvious. Note the light colored clypeus, a band of hardened, but flexible tissue between the eyes and the edge of the carapace where the fangs project outward. The fangs, or chelicerae, consist of a pair of stout basal structures (the prominent, blade-like portions on each side of the middle portion of the photo below--the one on the left is mostly obstructed by the spider's right-hand pedipalp) that move from side to side like scissor blades, with a long, slender, pointed structure at their distal ends (orange in color, and folded upward in the photo below, like a pocket knife) that penetrate the spider's prey. The hollow fangs have minute internal tubes that inject venom into the prey's body like a hypodermic needle
The ventral body of this spider shows a brightly marked sternum and the attachment of the pedipalps at modified coxae that serve as maxillae (the short pale structures at the base of the palps which assist the spider in masticating its food).
The ventral abdomen is brightly marked with yellow spots. A longitudinal yellow stripe adorns each side of the ventromedial abdomen, appearing much like the lighting of an airport runway that shows pilots where to land their aircraft. As the photo below shows, these bright markings seem to point toward the female's epigynum, and may serve as a visual aid that assists the male in locating and inseminating the female copulatory organs without undue fumbling.
The epigynum of the Argiope female is an external structure, consisting of a hardened, raised, plate positioned between the anterior book lung slits. These slits can be seen at the anterior ends of each yellow stripe (in the lower portion of the photo below), and stretch laterally from the epigynum (in the middle of that photo). The epigynum is the narrow projection that emerges between the lung slits and stretches backward, toward the spinnerets. Beneath the epigynum lies the gonopore (the primary genital opening for the female, seen here as a darkened depression directly under the epigynum, shallow posteriorly, but deepening anteriorly), that leads to the internal sperm ducts and thence to the seminal receptacles. The male inserts a pedipalp into the gonopore and deposits its sperm. The deposit occurs as a result of glandular secretions, hormonally produced in the pedipalp's embolus, that expel the sperm mass at the opportune time, i.e., only after the embolus has effectively threaded the sperm ducts. It is thought that these secretions also function to preserve the sperm until fertilization takes place later on.
The embolus of the male's pedipalp must match, in architecture, the female's convoluted sperm ducts, much as a key matches the form of the locking mechanism it fits. Otherwise insemination cannot occur.
Inasmuch as the copulatory architectures of disparate species of spiders do not correlate, the chance that a male of one species might successfully fertilize a female of another, and thus produce hybrid offspring, is so remote as to be practically impossible. I wonder, too, if the markings on the female's ventral abdomen, insofar as they uniquely delineate the positioning of the epigynum and, by reference, the underlying gonopore, play a part in facilitating successful mating within a species, while preventing disparate species from proceeding very far with any attempt at interbreeding.
The male must perform its work of insemination adroitly, to avoid irritating and thus inciting the wrath of an otherwise willing female. Apparently, the female is programmed to be receptive to a narrow range of foreplay maneuvering, and to reject, sometimes with malice of eternal consequence to the male (which, as you will notice by reading further, is only important to the male insofar as it prevents a successful insemination), any behavior that breaches its rigid standard of mating etiquette. Indeed, inept males of the same species tend to be removed from the gene pool the moment their incompetence is revealed. There is little doubt, then, that a male of another species who attempts to locate and deposit its sperm in the gonopore of a female whose abdominal markings do not instinctively guide it in its quest, would be at a distinct--and, methinks, quite dangerous--disadvantage.
There is much more to the story of mating in this species of orbweaver. Studies (for example, those carried out by Matthias Foellmer and Daphne J. Fairbairn), have shown that the primary object of male behavior is not the assurance of a long life, but the successful insemination of a single female in a manner that limits sperm competition from other males. A successful male who achieves insemination of its mate with one pedipalp will soon thereafter mate with the female again, this time inserting its second pedipalp into the epigynum. As soon as the female's sperm ducts have been threaded the male expels the bolus of sperm from the second pedipalp and, shortly thereafter, suffers a spontaneous and fatal cardiac arrest. The inserted pedipalp often breaks off later when the male's attached corpse is forcibly removed by the female. Though the impaled pedipalp does not entirely prevent subsequent inseminations by other males, it reduces their likelihood, and limits their effectiveness.
Many thanks to Stephen for these excellent photos!!!
* TERMITE ENCOUNTERS * SNAKE ENCOUNTERS * SNAKE BITE FIRST AID * SNAKE EXCLUSION * SPIDER ENCOUNTERS FOR 2008 * SPIDER ENCOUNTERS FOR 2007 * SPIDER BITE FIRST AID * SPIDER EXTERMINATION * PUSS CATERPILLAR ENCOUNTERS * PUSS CATERPILLAR FIRST AID * PUSS CATERPILLAR EXTERMINATION * Assembled & Edited by Jerry Cates. Questions? Corrections? Comments? BUG ME RIGHT NOW! ---- Ph: 512-331-1111 ---- E-Mail ---- Privacy ----BugsInTheNews * --0a0s--