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Southern black widow
(Latrodectus
mactans)
male & female 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.
The female of this species rests in the midst of its tangle, or cob, web, with its face upward and her two front legs (the longest) stretched out before her. If the male is present (despite her reputation for eating the male after they mate, the male can often be seen alive in the web, as discussed more completely below) he is usually positioned in a similar manner, but is smaller and less conspicuous than the female.
The web of the black widow is comprised of a dense, three-dimensional tangle of seemingly unorganized strands of silk. Silk produced by the black widow is unusually strong (so strong that it is sometimes used in microscope reticles and bombsight/rifle scope crosshairs). Though most of the strands are invisible (the original Lee "floating dot" rifle scope used spider web strands to suspend the dot, making it look as though it floats), their presence is immediately discovered by anyone who attempts to remove the visible remnants of a web from around a home (e.g., under the eaves, as in the above photo). A stick, poked into the mass of the web, seems suddenly grasped by a strong, invisible hand, that prevents its progress forward or from side to side. Unless one uses considerable force, the web wins the fight. Three structural levels exist in the webs constructed by the black widow. The uppermost section supports the web. Below this is a central region of tangle threads, with a lower section of vertical trap threads. The vertical trap threads are under tension and studded with sticky droplets; insects crawling through them break the strands and get entangled in them; as the trap threads separate from their anchor points, they lift their entrapped prisoner upward, toward the spider who waits in the central section of tangle threads. As the prisoner struggles to get free, it contacts and becomes stuck to even more of the surrounding trap threads. Its eventual immobilization by the threads is awaited, with patience, by the host spider, who then bites its prey and inoculates it with venom that The density of the three-dimensional web isn't obvious from a distance, but is made clear in the close-up photo, below.
Male black widow spiders are commonly found in webs alongside their mates. Cannibalism of the male by the female after mating is, in fact, rare among the three species of widow spiders found in the northern hemisphere. Such behavior may, however, be the norm for one or more of the widow species common in the southern hemisphere. The male in this web is notable for the dark streaks on its legs, which can be seen from a distance, and for the brown, rather than black coloration of its carapace and abdomen (often the male is black, with red spots on his abdomen, but this fellow's carapace and abdomen are tan to brown, without any of the shiny black features of the female. Remember that if you happen to read, elsewhere, that the male black widow is always black; color variations in spiders are not uncommon. Notice the distinguishing feature of the male spider (true for this species, and for most other species of spider as well), i.e., his swollen pedipalps. The enlarged palps--typical of the male but not in the female, whose pedipalps are slender structures--comprise the dark protuberances in front of the head. Pedipalps, though present in the female, are so small they are not easy to see, while those of the male are quite obvious. The distal ends of the male pedipalp are complex in architecture, and are used to transfer sperm to the female during mating.
What appears, at first glance, to be a second male in the web is, in actuality, only a shed skin. The male, shown above, recently molted, and this remnant of his former self remains in the web...
Go to Southern Black Widow Female Macroscopy, Page 1... ---------------------------------------------- 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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