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Southern Black Widow
Female
(Latrodectus
mactans) Photography and text by Jerry Cates The female of this species is highly venomous. Though timid and apparently lacking in any instinct to bite humans, it will bite if threatened.
I found this female in a web under an eave of a home in Jacksonville, Texas, on 12 April 2007. Many authorities state that black widows almost never build webs in the open, where they and their webs can be seen, but my experiences have run counter to that. In east and central Texas, where the black widow tends to be very common, the spider often spins webs under eaves, in crevices between bricks and masonry on the sides of homes, and in other equally open places. They are also often found inside electric junction and water service boxes, and in similar cryptic locations as well, so watch for them any time you open up such enclosures. I collected this spider in a specimen vial for study at the lab, and later took the macroscopic photos of various parts of its exterior anatomy. A close-up view of the carapace (the head and thorax) is shown below:
The eyes of the black widow spider, whether male or female, are arranged in two horizontal rows, of four eyes each, that stretch across the face of the spider's head. The row positioned highest on the head is the posterior row, and that positioned lowest on the head is the anterior row. In the black widow, the leftmost and rightmost eyes of each row (known as the anterior and posterior lateral eyes, or ALE and PLE) lie together, in a structure that protrudes forward, beyond the spider's face, such that the PLE faces to the side and back, while the ALE faces forward and downward. The eyes in the center of the anterior row (the anterior median eyes, or AME), are spaced in the lower surface of a protruding, elongated, horizontal structure above the chelicerae, and face downward, toward the chelicerae, or mouthparts, where prey is positioned during envenomation. The eyes in the center of the posterior row (the posterior median eyes, or PME) face upward.
The photo above provides a view of the ALE and AME of the female black widow, as seen from just beyond the tips of the spider's chelicerae. This is what the spider's prey would see just before the spider opened its jaws and lunged forward for the kill. In the photo below, the closed chelicerae are in focus, their sharp tips centered in the photo. As with all true spiders, the black widow's chelicerae are hinged so that they open and close laterally (from side to side) like scissors.
The red marking on the ventral abdomen of this specimen has a form whose posterior half is more reminiscent of a rounded rectangle than a triangle. As such, it conforms to the marking typical of the species Latrodectus mactans (Fabricus), the southern black widow. The ventral abdominal marking typical of the northern black widow, Latrodectus variolus (Walckenaer), consists of two separated red spots, the anterior spot having the form of a triangular solid, and the posterior mark having the form of a curved, elongated solid, similar to the lower half of the marking found on the abdomen of L. mactans, but with its posterior edge curved anteriorly. The western black widow, L. hesperus (Chamberlain & Ivie), has a single mark, like that of L. mactans, but with both halves in the form of solid triangles (joined as in a "true" hourglass), with the anterior triangle longer and broader than the posterior one.
The opening anterior to the red mark, shown in the above photo, is the spider's epigynum, ;which receives the male's pedipalp during copulation. Note the numerous small black hairs that cover the body. Though present, they are so minute as to give the impression that the spider's skin is entirely bald.
Go to Southern Black Widow MALE Macroscopy... ---------------------------------------------- The black widow spider is venomous, and its bite should be treated immediately at a medical clinic. We would like to hear of your experiences with such bites. We are also investigating the risk of secondary infections that may occur as a result of bites from other, otherwise harmless spiders whose venom is known to pose little or no danger to humans. In the process, we are collecting information on experiences persons have had with such spider bites. Please contact us about your personal experiences, if you have been bitten by this 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. The 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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