What You Should
Know About Spiders in Washington
~ THE WIDOW SPIDERS ~
The widow spiders, genus Latrodectus, are among the most recognized spiders on earth; they are the largest of the cobweb weavers, family Theridiidae, and all species are poisonous.
The term "widow spider" originated from the idea that the females devour the males after, or during, mating. This mate devouring behavior is somewhat a myth; while it may occur in captive situations, where the male cannot escape, it is uncommon in the field.
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There are five species in the United States, one in southern Europe, and additional species in Australia, the Near East, and South America. Widow spiders build strong, sloppy webs, in which the females usually remain, hanging upside down most of the time.
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Female widow spiders are bulbous and shiny in appearance, and may have bodies 12-16 mm long. Males are much smaller than the females but with longer legs. They are so different in appearance than females that they are rarely recognized as widow spiders by the lay person. Males are not considered a threat to humans, although they do possess venom and can bite.
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Juvenile widow spiders are usually light colored, and darken to their adult coloration gradually, with each successive molt of their exoskeleton.
The term black widow refers to those species in the United States, Europe, and some other areas, which are shiny black in appearance. The most well known of the U.S. black widows is the southern widow, Latrodectus Mactans, whose latin name translates "murderous biting robber".
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Like most widow spiders, it prefers dark, cool places to build its web, such as outhouses, window wells, under well covers, and beneath trash. The red "hourglass" of the southern widow is actually shaped more like an anvil than a perfect hourglass in most specimens.
The western black widow, Latrodectus Hesperus, ranges from extreme southwestern Canada, south into Mexico, and east to west Texas. Hesperus is the common black widow of the western United States, and is abundant in regions of Arizona, California, and other westerly locales.
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One of its favored natural habitats is in abandoned rodent holes, but it is often found around human habitations, even in the "downtown" districts of many western U.S. cities. The western widows' general appearance is very similar to that of the southern widow; the "hourglass" marking in the western widow is usually shaped like a perfect hourglass, though it is divided into two seperate "spots" in some specimens. Like its southern cousin, the western widow causes a large number of bites, particularly in the southern part of its range.
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Bites by widow spiders often are initially painful, but sometimes are not felt. The local dermal reaction is minimal, usually consisting of little more than an area of erythema (redness) around the bite site, which disappears within several hours; no tissue necrosis occurs following bites by widow spiders. A potent neurotoxin in the venom induces the disease state latrodectism, which manifests itself with severe muscle cramping and spasms; the cramping usually begins in the large muscle masses of the legs, or the abdomen. The abdomen can exhibit a board-like rigidity, and the pain has been compared to that of acute appendicitis, and to childbirth.
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Some widow bite victims experience anxiety, profuse sweating, nausea, piloerection (hair standing on end), increased blood pressure, and other unpleasant manifestations. Paralysis, stupor and convulsions, as well as psychological abnormalities may occur in severe cases.
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Death can occur in a small percentage of cases, particularly when the victim is a small child or elderly person.
Persons bitten by widow spiders usually present themselves to medical facilities voluntarily, as a result of intense pain. The treatment for widow spider bites may vary, according to the age of the victim and the severity of the poisoning: The most common effective treatment is the intravenous administration of the muscle relaxant calcium gluconate, often requiring several courses of treatment to abate the cramping and spasms: Robaxin (Methocarbamol) has been used successfully in cases that did not respond well to calcium gluconate.
Antivenin (antivenom or antivenene in some countries) is produced against the venom of widow spiders in Australia, Europe, South Africa, and the United States.
It can be used in severe cases, which do not respond to muscle relaxant therapy, or where the victim's life is at risk.
As with most spiders, black (and other) widow spiders bite humans only in accidental situations: Widow spiders are practically blind, and spend most of their lives in the web.
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Hobo Spiders
HOBO SPIDER NATURAL HISTORY
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The hobo spider, Tegenaria Agrestis, is a member of the family of spiders known as the Agelenidae or funnel web weavers. Approximately 500 species of funnel web weavers occur worldwide; about 300 of these are found in North America, and about 100 species are native to Europe. Funnel web weavers are characterized by their ability to move rapidly, and by their layered, flat web, which has a funnel-like lair at the rear in which the spider resides and waits for prey. The web is not sticky like that of many spiders, but rather is a trip web, which traps insect prey that is unable to navigate on the surface.
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The genus Tegenaria contains those spiders which are commonly known as European house spiders, although not all are European, and some do not live in houses; about 90 species are recognized. Some species of European Tegenaria have extended their range far beyond the European continent: The domestic or lesser house spider, Tegenaria Domestica, is now cosmopolitan, and is common in and around human habitations in many areas of the world. In the United States the giant house spider, Tegenaria Gigantea, is now found in the Pacific Northwest, and Tegenaria Pagana is now established in some southern and western states.
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Tegenaria Agrestis, the "hobo spider", was first described in 1802 by naturalist C.A. Walkenaer, in the Paris based journal Faune Parisienne, (vol. 2, pp. 187), under the name Aranea Agrestis, which translates spider of the field. This reference to the field was accurate for the species in its indigenous range (western Europe), where the spider lives in fields, woods and rock quarries. While in Europe the hobo spider is occasionally found in greenhouses, it is largely divorced from the human population on that continent.
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The hobo spider was first reported in the U.S. in 1936 by arachnologist Harriet Exline (as Tegenaria Magnacava), who published her findings in the journal Psyche, vol. 43(1), pp. 21-26. In the United States, the introduced hobo spider did not seek the same type of habitat favored by its European counterpart: Rather, it became established around human habitations, and is now commonly found around the foundations of houses, and beneath rocks, wood, and ornaments in yards. Recently, U.S. specimens of hobo spiders have been found in rural areas, including some heavily farmed areas; this trend may continue, placing some U.S. populations of this spider in habitats similar to those that it occupies in Europe. It is unlikely that this trend will affect populations in urban areas. Urban populations of hobo spiders do appear to be decreasing in some areas, such as Seattle, Washington, where the giant house spider, Tegenaria Gigantea, has become abundant.
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The life cycle of the hobo spider in the United States has not been conclusively established, as controlled laboratory studies on this topic have not been reported. Some arachnologists believe that west coast populations are annuals, completing the entire life cycle in one year. Inland populations were originally reported in the literature to undergo a two year life cycle; however, three distinct stages (small juveniles, medium sized immatures, and adults) can be found during the late summer and early fall in inland areas, suggesting that inland populations may actually have a life cycle of three years. The eggs of the hobo are deposited in one to four egg cases in late September and October. These egg cases are composed of several layers of silk, intermingled with layers of soil and debris. The egg cases are usually attached to the undersides of rocks, wood, or other items found in yards, gardens and vacant lots; each egg case may contain 100 or more eggs. Contrary to some references hobo spiders are not prone to construct egg cases inside living quarters (though they have been found in crawlspaces). The eggs hatch in early to mid-June: The spiderlings emerge, feed, and largely remain beneath the surface during their first season, molting their exoskeleton periodically as they grow. The juvenile spiders then overwinter, and are sometimes found indoors during this period. Assuming the two year scenario, the spiders emerge as adults in late July to early August of the second year. The females build webs and remain stationary, but the males began nocturnal wanderings in search of mates. It is at this juncture that males enter houses (often in large numbers) from outside habitat and from garages and crawl spaces; thus, they come into contact with humans; most bites occur during this time period. The hobo spider season peaks during the first week or two of September in most areas. After mating the males began to die, and are absent by the first week of October. The females construct the egg cases, and most remain in the web until they die, usually expiring by mid-November: Some adult females do enter houses in late September, October, and November.
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The behavioral aspects of the hobo spider have been a subject of controversy in the past, primarily due to the the publicized myth of the "aggressive house spider". While the hobo will bite when pressed against skin or tormented, it is no more "aggressive" than other wandering spiders; it does not bite without clear provocation, and certainly does not track people down and attack them, as some people have come to believe. The quick movements of this spider, and the fact that they sometimes run toward individuals when disturbed have fueled such myths, but the idea that such spiders are "attacking" is a misinterpretation. In actuality, these spiders have very poor vision and cannot distinguish objects more than a foot or two away. When disturbed inside a house, particularly when a light has just been turned on, the spiders most often remain stationary. When such spiders finally sense potential danger, they run, sometimes toward a person that they really can't see. Hobo spiders are not good climbers, and are usually found at ground or basement level. They sometimes climb up to a level of about four feet if the surface of the wall, etc. is sufficiently porous. Hobo spiders found in wash basins and bathtubs arrived there by falling down the slick porcelain surface; they did not come up through the drain.
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Physically, the adult hobo spider is a moderately large (12-18 mm body length) brown spider, with long, unmarked legs (legs included, a typical specimen would fit nicely on a silver dollar). The dorsal abdomen exhibits a "herringbone" or multiple chevron pattern, which may be quite obscure in darker individuals. The male sports two pedipalps (antennae like protuberances) between the two front legs, which are swollen at the ends, looking somewhat like a pair of boxing gloves; these "boxing gloves" are actually the male genitalia, not "fangs" or "poison sacs". The female generally has a larger abdomen than the male, and does not have swollen "boxing gloves" at the ends of the pedipalps. Several other spiders resemble hobo spiders; only an arachnologist, or other specifically trained person should attempt to make a positive identification of this species: In an instance where a spider has bitten a person, it is imperative to obtain positive identication only from a qualified professional arachnologist.
HOBO SPIDER POISONING (TEGENARISM)
Spider venom poisoning constitutes a disease state characterized by a set of signs (observable physical or objective evidence of disease) and symptoms (complaints that the bite victim relays to the physician, etc.), which lead to the diagnosis of spider envenomation. Traditionally, disease states induced by spider bite have been assigned specific names, according to the genus of spider which causes the poisoning. For example, poisoning by the widow spiders (genus Latrodectus) is termed latrodectism, while poisoning by the recluse spiders (genus Loxosceles) is known as loxoscelism; thus, poisoning caused by the hobo spider, Tegenaria agrestis, may be properly termed tegenarism. While not all species in any given spider genus may induce significant poisoning, and while signs and symptoms may differ from species to species in a genus, this nomenclature has proven useful in categorizing different types of spider envenomation.
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Hobo spider poisoning (tegenarism) does not invariably develop following a bite by a hobo spider. A large percentage (perhaps 50% or more) of defensive bites by the hobo are "dry", and no venom is injected when the spider bites (see A Word About Bites and Stings for more on this). Hobo spiders, like many other venomous creatures, are more likely to incorporate venom in a food getting bite than in a defensive bite. Typically, defensive bites by the hobo spider are lightning fast, the spider opening its scissor-like fangs, closing them together into the tissue of the victim, and then withdrawing rapidly. Very often the bite itself is painless, although this varies depending upon the circumstance and location of the bite, and upon the psychological state of the victim. Most spider bites are single, not in rows or patches like those of some parasitic arthropods; multiple bites do occasionally occur, such as when the spider is trapped between skin and clothing, and cannot escape.
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When envenomation does occur from the bite of a hobo spider, local and/or systemic manifestations may appear. The severity of these phenomena are dependent to a degree on the age and sex of the biting spider: In laboratory experiments the venom of the male hobo spider produces more severe effects than that of the female, and evidence exists suggesting that the venom of subadults may be more toxic than that of adults. The local effects, which appear following most hobo spider envenomations, represent a type of necrotic arachnidism, which is almost identical to the local effects produced by brown recluse spider, Loxosceles reclusa, poisoning. Typically, immediately following envenomation, a large (several cm.) area of redness (erythema) forms around the bite site: This usually disappears within a few hours, leaving a small reddish induration (hardened area), which is not dissimilar to the classic "mosquito bite". Within 24 to 48 hours blistering may occur at the bite site. Within an a additional 24 hours these blisters may rupture, leaving an open ulceration. Within a few days of ulceration, if left uncovered, eschar or "scab" formation begins to develop over the lesion. By three weeks post-bite this becomes pronounced giving the lesion a "target and bulls-eye" appearance. Following this, the "scab" is sloughed and the lesion generally heals, leaving a scar, within 45 days of the original bite. In some instances, particularly when the bite is delivered in an area of fatty tissue, such local lesions may become deep and extensive, and may not heal for two to three years.
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Other long-term physical effects, such as intractable burning pain, damage to blood vessel valves, and cyst formation occasionally occur in conjuntion with local lesion development. The lesion that results is sometimes oblong or multiple, resulting not from more than one spider bite, but rather from gravitational drift, which moves venom components downward, away from the bite site. The process which causes the local phenomenon of necrotic arachnidism involves circulatory disturbances which result in ischemia, or lack of adequate blood flow in the affected tissues. Following venom injection, rapid coagulation of blood occurs in the smaller blood vessels of these tissues. This produces a centralized area which does not receive enough blood, and the area literally dies as a result of oxygen starvation.
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Systemic, or generalized effects are seen in about 45% of persons envenomated by hobo spiders. The most common reported symptom is severe headache, which usually does not respond to over the counter analgesics (aspirin, which can prolong bleeding time, should not be used for hobo spider bite induced headaches). In addition to this, victims may experience a dry mouth, nausea, weakness and lethargy, dizziness, visual disturbances, hallucinations, joint pain and/or other undesirable effects. As with many types of complex poisoning, most victims of systemic tegenarism do not experience all of these phenomenon, but that is dependent upon the severity of the poisoning. About 15% of envenomated subjects are poisoned severely enough to require hospitalization: In rare cases aplastic anemia (bone marrow failure) can develop several weeks after the bite, which results in a fatal outcome. Another rare but dangerous condition that has been seen following hobo spider envenomation is the development of severe intractable vomiting accompanied by secretory diarrhea.
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Some cardinal rules apply to persons that have been bitten by, or think that they have been bitten by a venomous spider. Above all, if you are bitten by any spider, and actually catch the spider in the act, always capture the spider for identification by a qualified arachnologist. Never discard a spider that has definately bitten a human. In the case of the hobo spider, not only is positive species identification important, but so is a determination of the spiders sex and age; these factors can help predict the severity of potential poisoning, and assist the attending physician in charting a course of treatment. Preserve the spider (or whatever parts of it remain) and take it to the clinic with you. If you suspect that you have been bitten by a dangerously venomous spider, see a physician. Most suspected spider bites in the United States turn out to be other conditions. The vast majority of spiders are harmless and beneficial.
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©1999 Darwin K. Vest, Eagle Rock Research
