Gary R Mullen Lactrodectism

The term latrodectism, also known as neuromyopathic animism, is a syndrome caused by the bite of any of several Latrodectus species. The venom of these spiders contains potent neurotoxins which cause generalized pain, nausea, vomiting, faintness, dizziness, perspiration, and neuromuscular involvement in the form of muscle weakness, stiffness, cramps, tremors, incoordination, numbness or prickling sensations, paralysis, disturbed speech, and difficulty breathing. The main toxic fraction of the venom of Latrodectus mactans is a protein called a-latrotoxin, which acts on the motor nerve endings at the neuromuscular junctions. It causes depletion of the synaptic vesicles and the selective release of neurotransmitters that cause contraction of voluntary muscles. The autonomic nervous system is also affected. In severe cases the victims typically experience painful abdominal and leg cramps, profuse sweating, lachrymation, and spasms of the jaw muscles that distort the face and cause grimacing. Although symptoms often appear within 10—60 min, the syndrome may take several hours to develop; symptoms usually persist for 20—48 hr. A diagnostic sign of latrodectism is sweating at the bite site. This may be accompanied by localized swelling and redness, increased blood pressure, and the development of various types of rashes, either generalized or limited to the bite area. The fatality rate is relatively low (< 5%) even in untreated cases.

Prompt treatment of Latrodectus bite victims significantly reduces the severity of symptoms and promotes recovery. Where practical, a tourniquet can be effective if applied within a few minutes after the bite to reduce spread of the venom. Immersing the body in a hot bath and administering morphine or muscle relaxants help to alleviate the pains and cramps. Particularly effective is the intravenous administration of a 10% solution of calcium gluconate or calcium lactate in saline, which affords welcomed relief in reducing muscle spasms and hypertension. Antivenin can be very effective as a treatment, especially in cases involving L. mactans. Alcohol should never be taken by the victim at any time during the course of the illness. Children are more likely to have serious reactions to Latrodectus bites and should receive medical attention as quickly as possible.

There are 16—30 species of Latrodectus worldwide; the number varies according to different taxonomists (Levi, 1959). Although there is evidence to support the recognition of several subspecies of L. mactans (e.g., L. m. hasselti, mactans, menadovi, and tredecimguttatus), these taxa are treated here as separate species. As a group they are medium-sized spiders, seldom more than 1.3 cm in body length, with globose abdomens and relatively long legs. They are generally recognized by their shiny black color and a red or orange hourglass marking on the underside of the abdomen. Some species, however, are more drab in appearance, or they may be colorfully patterned, as in the case of L. bishopi. They are known by a variety of common names in different parts of the world. In North America they are usually called black widow spiders and, less commonly, hourglass spiders or button spiders. The term "widow" is derived from the misconception that the females invariably devour the male after mating, whereas the term "button" refers to the resemblance of the shiny black, round abdomen of the female to the buttons on old-fashioned shoes. Other common names include shoe-button spiders in South Africa; jockey in Arabia; karakurt (black wolf) in Russia; night stinger or katipo in Australia and New Zealand; la malmignatte in the Mediterranean region (notably Italy and Corsica); araña capulina, chintatlahua, and viuda negra in Mexico; cul-rouge and veinte-cuatro horas in the West Indies; lu-cacha in Peru; mico in Bolivia; guina and pallu in Chile; and araña del lino (flax spider), araña del trigo (wheat spider), and araña rastrojera (stubblefield spider) in Argentina and other parts of South America.

Latrodectus species are shy, retiring spiders which construct their tangled webs of coarse silk in dark, undisturbed places, usually close to the ground. They are especially common under logs and stones and in abandoned animal burrows, crevices in protected earthen banks, and various materials stacked on the ground. Some species, however, build large, irregular aerial webs in shrubs and other vegetation, often up to a meter or more above the ground. The adults are primarily nocturnal, spending most of the day in the security of their silken retreats in protected recesses adjoining the web. Prey consists primarily of medium- to large-sized insects and other arthropods which stumble into the web.

Following mating, the female constructs one or more egg sacs, which she suspends in the web. Each sac typically contains 200—250 eggs. The total number of egg sacs produced by a given female varies considerably among species, with up to 10 for L. mactans and 20 for L. hesperus. The egg sacs are usually spherical or pyriform, white or grayish, with a tough, tightly woven outer covering. The eggs hatch in 14—30 days. The spiderlings undergo their first molt within the sac 3—4 days after hatching and then emerge via one or more tiny holes which they cut through the silken layers. The spiderlings remain in their mother's web for several weeks before dispersing. They undergo 4-9 molts, depending on the species and sex. Males reach maturity in 2—5 months, whereas females require somewhat longer, usually 3.5—8 months.

Spiderlings of Latrodectus species look quite different from the adult females. Young spiderlings are pale colored with light and dark stripes on the abdomen and legs. They often exhibit patterns of white, yellow, and red bands and spots, which are gradually lost in the females as they mature. The males, however, tend to retain the color pattern of the immatures, including the abdominal markings and leg bands. Upon reaching sexual maturity, the males leave their webs to wander in search of a female. Mating takes place in the female's web. Contrary to popular belief, females of most Latrodectus species do not kill and devour the males following insemination any more frequently than do most other spiders. In fact, in the case of L. bishopi the adult male and female actually live together in the same web.

Five Latrodectus species occur in North America: L. bishopi, L.geometricus, L. hesperus, L. mac-tans, and L. var-iolus. L, mactans is the most venomous and widespread of these species, causing most of the cases of lactrodec-tism requiring medical attention. L. tredecimguttatus is the most important species in Europe, whereas L, cura-caviensis, L. hasselti, and L. katipo are important species in South America, Australia, and New Zealand, respectively.

Red widow (Latrodectus bishopi) This is the most colorful of the North American widow spiders. The cephalothorax and legs are orange or reddish, contrasted with a black abdomen which has red or orange spots with yellow borders. Rarely is the abdomen all black, It lacks the characteristic hourglass found in most Latrodectus species. Instead, the marking is pale and usually reduced to a transverse bar or a single triangular spot, representing one-half of an hourglass (Fig, 22.16). The red widow is known to occur only in the sand-pine scrub habitat of peninsular Florida. There it often builds its web in palmettos (Aracaceae), forming its cone-shaped, silk-lined retreat in a folded or rolled leaf frond which it ties together with silk. The snare itself is commonly 1-2 m above the ground, extending as a large, tangled web amidst the fronds to

FIGURE 22.16 Red widow spider, Latrodectus bishopi (Theridiidae), female, ventral view. This widow spider is unusual in Sacking the red hourglass marking; the marking is typically reduced to a transverse bar or a single, triangular spot. (From Short and Castner, 1992, courtesy of University of Florida-IFAS.)

FIGURE 22.16 Red widow spider, Latrodectus bishopi (Theridiidae), female, ventral view. This widow spider is unusual in Sacking the red hourglass marking; the marking is typically reduced to a transverse bar or a single, triangular spot. (From Short and Castner, 1992, courtesy of University of Florida-IFAS.)

Window Glass Gun Shot Pictures
FIGURE 22.17 Brown widow spider, Latrodectus geometricus (Theridiidae), female, dorsolateral view. (Photo by Sturgis McKeever.)

form, in part, a horizontal silken sheet reminiscent of sheet-web spiders. Very little is known about the potency of L. bishopi venom, and no bite cases have been documented.

Brown widow (Latrodectus geometricus) As its common name implies, L. geometricus females are brownish, rather than black, and have a highly variable color pattern that gives it a mottled appearance (Fig. 22.17). Typically there are three pairs of irregular-shaped spots along the dorsal midline of the abdomen. These vary from simple white spots with black borders to multicolored bull's-eye spots marked with white, yellow, orange, reddish brown, tan, gray, or aqua. The hourglass is generally dull orange, complete, and commonly bordered with yellow. Occasionally individuals are nearly black, more closely resembling other widow spiders.

The brown widow occurs most commonly throughout Brazil and along the eastern coast of South America. From there it has spread by cargo ships and other means of commerce to many other parts of the world, and it is now widely distributed in the Tropics. Introductions have led to established populations in peninsular Florida and Hawaii. This spider is found in a wide range of domestic settings in or near buildings, It constructs a relatively small tangled retreat in corners and chinks of brick and cement walls, building foundations, and fences, under overhangs of steps, and along street curbs. In addition to urban areas, L. £jeometricus is common in South America along ocean beaches, where it seems to prefer to construct its web in low, running plants such as the morning-glory Ipomoea biloba (Convolvulaceae) above the high-tide mark. It is even more shy than other widow spiders, is not aggressive, and rarely has been recorded biting humans. Some authors regard it as the least dangerous of the five widow spiders in North America.

Southern black widow (Latrodectus mactans)

This is the most notorious of all venomous spiders because of its potent venom, widespread occurrence, and likelihood of coming into contact with humans and domestic animals. It is found throughout eastern North America from southern New England to eastern Mexico. It also occurs in the Bahamas, West Indies, South America, southern Europe, eastern Arabia, India, Australasia, the Pacific region in general, and Hawaii. The adult female typifies the general description of Latrodectus in being shiny black with a prominent red hourglass on the underside of the abdomen (Fig. 22.18). It usually has a small red spot just above the spinnerets and occasionally a median series of additional red spots extending anteriorly onto the abdominal dorsum. It is found outdoors in various protected places under rocks, logs, boards, and other ground debris and frequently near buildings. Unlike the other La-trodectus species in North America, L. mactans also occurs indoors in barns, wood sheds, garages, and various other unheated storage areas. Before the days of indoor plumbing, the widespread use of outdoor privies contributed significantly to the number of human cases of envenomation, especially in males bitten on the genitalia by black widow spiders in webs under the toilet seats.

Although the bite of L. mactans may go unnoticed in some cases, it is more commonly felt as a pinprick or an immediate sharp, burning pain with little or no swelling. The pain spreads from the bite site to regional lymph nodes and other parts of the body, usually reaching its maximum intensity in 1-3 hr, Thereafter the

FIGURE 22.18 Southern black widow spider, Latrodectus mactans (Theridiidae), female, ventral view, showing characteristic red hourglass marking. (From Gertsch, 1979.)

pain may be continuous or intermittent, lasting up to 48 hr. The accompanying muscular spasms and cramps, especially in the abdomen and legs, can lead to tightness of the chest, boardlike rigidity of abdominal muscles, and complete prostration. In extreme cases, complications may occur in the form of shock, leukocytosis, and lesions of the liver, spleen, and kidney, evidenced by blood and elevated protein levels in the urine. The death rate can be as high as 4-5% in untreated cases, the highest of all Latrodectus species.

Northern black widow (Latrodectus variolus)

The northern black widow closely resembles L. mac-tans in both size and general appearance. It is usually distinguished, however, by the ventral hourglass being divided into two transverse bands and a row of prominent red spots along the dorsal midline of the abdomen. Its geographic range largely overlaps that of L. mactansm North America; it occurs widely throughout the eastern United States as far south as western Florida and eastern Texas. It is more common in the northern states, extending into southeastern Canada. Unlike L. mactans, it seldom is found in buildings, preferring outdoor situations such as old stumps, piles of dead tree branches, hollow logs, abandoned animal burrows, cavities in rock walls, and under debris. It is common in wooded areas, where it constructs a large tangled web in shrubs and tree branches, sometimes as high as 6 m above the ground.

Western black widow (Latrodectus besperus)

This species also is very similar in appearance to L. mactans. The abdominal dorsum is typically ail black, only infrequendy having red markings. The ventral red hourglass is well defined and usually complete. It occurs from Oklahoma, Kansas, and central Texas into the southwestern United States and adjacent Mexico. It also is found in Israel as an introduced species. The western black widow utilizes a wider range of habitats than L. mactans. It most commonly constructs its web near the ground, in animal burrows, or under various objects. However, it also is found above the ground in shrubs and trees and in such places as grape arbors and bird nests. It is well adapted to semiarid and arid habitats, where it can be found in soil crevices and various desert plants such as agaves and cacti.

European black widow (Latrodectus tredecimguttatus) L. tredecimguttatus is the most common widow spider in Europe. It occurs primarily in the Mediterranean region, extending eastward into Eurasia. In Italy and Corsica it is called la malmignatte, and in Russia, karakurt, or "black wolf." It occurs exclusively outdoors, where it constructs its web in a variety of herbaceous and shrubby vegetation, including cultivated

FIGURE 22.18 Southern black widow spider, Latrodectus mactans (Theridiidae), female, ventral view, showing characteristic red hourglass marking. (From Gertsch, 1979.)

trash cans, and gas-meter boxes. Although this spider is not aggressive, the female causes a painful bite that can lead to systemic envenomation and fatalities (ca. 5%) if untreated. In typical cases, the initial bite is relatively painless, comparable to a pinprick. Thereafter the pain intensifies from a few minutes to a half hour, often accompanied by localized perspiration and edema, nausea, and vomiting. Localized sweating at the bite site is an important diagnostic sign (Wiener, 1961). In untreated systemic cases, recovery is usually protracted and may take 3—4 weeks. The severity of red-back spider bites was dramatically reduced in Australia with the introduction of an antivenom against L. hasselti in 1956; since that time, no fatalities have been recorded.

crops and arbors. This species poses a significant occupational hazard for farmers and field workers, who are commonly bitten while harvesting or threshing wheat, handling hay, picking fruit, or working in vineyards.

Araña del trigo (Latrodectus mracaviensis)

In South America, L. curacaviensis is frequently encountered by humans in buildings, garages, and privies. It also is found in cultivated crops such as wheat, accounting for its common name araña, del trigo, or wheat spider. It closely resembles L. mactans, with which it is easily confused. Like L. mactans, its bite can cause serious illness and death.

Australian red-back spider (Latrodectus hasselti)

Females of this Australian species are 2—3 cm long. They are black with a prominent red stripe along the dorsal midline of the abdomen (Fig. 22.19), hence the common name red back. Some authors regard this spider as a subspecies of L. mactans. It occurs in sheltered, preferably dry sites such as hollows of trees and under Logs and rocks. It often builds its retreat and web around building foundations and in ventilator gratings,

FIGURE 22,19 Australian red-back spider, Latrodectus hasselti (Theridiidae), female, dorsal view, showing characteristic, wide, reddish stripe along dorsal midline of abdomen. (Photo by G. R. Mullen.)

Katipo spider (Latrodectus katipo) This spider is primarily a coastal species found high on ocean beaches and in river beds under driftwood or at the base of vegetation. It occurs in the Caribbean region (Jamaica, British West Indies) and New Zealand, where it is known as the New Zealand redback.

Under certain circumstances spiders can pose health threats to household pets, livestock, and other domestic animals. Most cases occur either in stables or in pasture situations where animals are grazing. In the latter situation, a high density of a venomous species can cause significant veterinary concerns. Although the evidence of spider bites in nonhuman animals often is circumstantial, enough cases have been documented to show that theridiid and theraphosid spiders are the more common causes of serious spider bites of veterinary importance.

Most cases of envenomation by spiders in grasslands and pastures are caused by Latrodectus species. They usually occur in localized areas where populations of certain venomous taxa are high. Outbreaks involving L. erebus were reported in the steppes of southern Russia in the 1830s. Grazing animals were severely bitten, causing some to stampede due to the pain and to run until they dropped. Fatalities as high as 12% in sheep, 17% in horses, and 33% in camels were reported (Motchoulsky and Becker, 1855). Notable outbreaks oflatrodectism affecting cattle and agricultural workers also occurred in Spain in the 1830s and 1840s and caused deaths in horses, sheep, and other livestock in Chile in the 1870s. For other examples of latrodectism involving goats, sheep, catde, and horses in Europe, South Africa, and Indonesia, see Maretic and Lebez (1979). Latrodectism does not seem to present a significant problem for livestock in North America or South America.

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