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Figure 4.4 SPIDERS AND HARVESTMEN. (a) Huntsman spider (Heteropoda venatoria, Heteropodidae). (b) Black widow (Latrodectus mactans, Theridiidae), female, (c) South American violin spider (Loxosceles laeta, Loxoscelidae). (d) Harvestman (Prionostemma sp., Gagrellidae). (e) Harvestman (Gonyleptus janthinus, Gonyleptidae).

Figure 4.4 SPIDERS AND HARVESTMEN. (a) Huntsman spider (Heteropoda venatoria, Heteropodidae). (b) Black widow (Latrodectus mactans, Theridiidae), female, (c) South American violin spider (Loxosceles laeta, Loxoscelidae). (d) Harvestman (Prionostemma sp., Gagrellidae). (e) Harvestman (Gonyleptus janthinus, Gonyleptidae).

tan in distribution, probably introduced from Asia. It is very common in human habitations throughout the warm lowlands of Latin America. Here it is valued as a predator of cockroaches, and it is known at times also to kill and eat scorpions and even small bats. Some details of its life history have been elucidated (Ross et al. 1982). It is capable of producing a faintly audible buzz or hum by means of leg oscillations while coupled to the substratum by tarsal adhesive hairs; the sound apparently plays a role in courtship (Rovner 1980).

References

Muma, M. H. 1953. A study of the spider family Selenopidae in North America, Central America, and the West Indies. Amer. Mus. Nov. 1619: 1-55.

Ross, J., D. B. Richman, F. Mansour, A. Trambarulo, and W. H. Whitcomb. 1982. The life cycle of Heteropoda venatoria (Linnaeus) (Araneae: Heteropodidae). Psyche 89: 297-305.

Rovner, J. S. 1980. Vibration in Heteropoda venatoria (Sparassidae): A third method of sound production in spiders. J. Arachnol. 8: 193-200.

Widow Spiders

Theridiidae, Latrodectus. Spanish: Viudas negras (General); aranas naranjas (Venezuela); cul rouge, 24-horas (West

Indies); lucachas (Peru); guiños, pallus (Chile); huyuros micos (Bolivia); rastrojeras, arañas del lino (Argentina); arañas capulinas, po-ko-moo (Mexico); arañas bravas (southern South America). Nahuatl: Tzintlatlauhqueh, sing, tzintlatlauhqui (var. chintatlahuc).

Female "black widow" spiders (Latrodectus mactans) are medium-sized (BL 8—15 mm) and jet black, with a large, naked, globose abdomen having a characteristic reddish hourglass marking on the underside (fig. 4.4b). In other species of the genus, the background color may vary from white to reddish-brown, with beautiful red and yellow lines or spots adorning the dorsum. The males are four to five times smaller but with legs almost as long as the females'. The eight eyes are in two rows.

All are widely feared for their venomous qualities. Indeed, they bear a highly potent neurotoxic venom (Bettini and Maroli 1978). Symptoms of the bite begin with a sharp local pain that gradually moves from the wound area to other parts of the body, concentrating finally in the abdomen or legs. Other effects are nausea, dizziness, fainting, and shock, occasionally with a fatal outcome. In spite of the potential seriousness of envenomization by these spiders, they are reluctant to bite or to inject much venom so should not be considered really dangerous.

Because of their medical importance, they have been investigated more than other spiders, particularly in Argentina, where the several species are now fairly well studied embryologically (González 1981, 1984) and ecologically (Schnack et al. 1983, Estévez et al. 1984). They are controlled naturally by predaceous mud and spider wasps (Sphecidae, Pompilidae) and parasitoids among the chalcidoid wasps (Desantisca, Eurytomidae) and chloropid flies (Pseudogaurax) (Pérez Rivera 1980, Sabrosky 1966).

Black widows are shy and largely nocturnal. During the day, they rest in their finely threaded, amorphous webs, which they construct in protected, cool, dry, dark retreats. These are often soil fissures or spaces among debris, in wood piles, refuse piles, or under houses (Anderson 1972).

The taxonomy of these spiders is difficult and still unsettled owing to their great variability and overlap in structural features. Levi (1959) once recognized only three basic species, L. mactans, L. geomet-ricus, and L. curacaviensis, but he concedes that this is an oversimplification and that there are probably several Latin American species (Levi 1983). Various other species have been described (Carcavallo 1959) and reclassifications proposed (see review of Bettini and Maroli 1978: 149f.), but the genus Latrodectus is in need of a complete revision using modern analytic techniques.

References

Anderson, M. P. 1972. Notes on the brown widow spider, Latrodectus geometricus (Ara-neae: Theridiidae) in Brazil. Great Lakes Entomol. 5: 115-118. Bettini, S., and M. Maroli. 1978. Venoms of Theridiidae, genus Latrodectus. In S. Bettini, ed., Arthropod venoms. Springer, Berlin. Pp. 149-212.

Carcavallo, R. U. 1959. Una nueva Latrodectus y consideraciones sobre las especies del género en la República Argentina (Arach. Theridiidae). Neotropica 5: 85—94.

Estf.vez, A. L., A. González, andJ. A. Schnack. 1984. Estadísticos vitales en especies Argentinas del género Latrodectus Walckenaer (Aran-eae, Theridiidae). II. Latrodectus antheratus (Babcock), Latrodectus corallinus Abalos y Latrodectus diaguita Carcavallo. Physis, Sec. C, 42(102): 29-37.

González, A. 1981. Desarrollo postembrionario de Latrodectus mirabilis, Latrodectus corallinus y Latrodectus antheratus (Araneae, Theridiidae). Physis, Sec. C, 39(97): 83-91.

González, A. 1984. Desarrollo postembrionario y evolución de los órganos mecanorreceptores de Latrodectus diaguita Carcavallo, y estudio de la tricobotriotaxia de Latrodectus quartus Abalos (Araneae, Theridiidae). Physis, Sec. C, 42(102): 1-5.

Levi, H. W. 1959. The spider genus Latrodectus (Araneae, Theridiidae). Amer. Micro. Soc. Trans. 78: 7-43.

Levi, H. W. 1983. On the value ofgenitalic structures and coloration in separating species of widow spiders (Latrodectus sp.) (Arachnida: Araneae: Theridiidae). Naturwiss. Ver. Hamburg Verh. (n.f.) 26: 195-200.

Pérez Rivera, R. A. 1980. Distribución geográfica, potencial reproductivo y enemigos naturales de la viuda negra en Puerto Rico. Carib. J. Sei. 15: 79-82.

Sabrosky, C. W. 1966. Three new Brazilian species of Pseudogaurax with a synopsis of the genus in the Western Hemisphere (Díptera: Chloropidae). Dept. Zool., Sec. Agrie., Säo Paulo, Pap. Avul. 19: 117-127.

Schnack, j. A., A. González, and A. L. Estévez. 1983. Estadísticos vitales en especies Argentinas del género Latrodectus Walckenaer (Araneae, Theridiidae). 1. Latrodectus mirabilis Holmberg. Neotropica 29(82): 141-152.

Violin Spiders

Loxoscelidae, Loxosceles. Spanish: Aranas de las rincones (Chile).

Loxosceles are shy, sedentary spiders that occupy a wide variety of dark, secretive habitats in natural and domestic situations, usually rock crevices or hollows under rocks, under debris and loose bark, or at cave entrances. They are common in corners and niches in adobe brick houses and other domestic structures. Their irregular webs are large, with thick, very sticky threads. They usually remain on their webs, which they continue to enlarge as long as they live.

Violin spiders carry a venom capable of severely injuring humans (Schenone and Suarez 1978). The venom's tissue-destroying capability has been well established. Clinical signs from bites range from mild necrosis to systemic reactions but rarely death. Although the venomousness of only a few species is recorded, it appears that all species of the genus are toxic. Shy and retiring, they never come forth to bite intentionally. Cases of envenomization, "loxoscelism" (Biicherl 1961), are normally only caused by specimens that have accidentally crawled into beds or onto clothing and that have bitten in defense when compressed.

These spiders are recognized by their small to medium size (BL 5—20 mm), light to medium-brown color, and long, thin legs. The back of the carapace often carries a dark outline in the shape of a violin. They are unique in having the six, equal-sized eyes forming a transverse row, in three diads. The legs and body are thickly clothed with abundant, fine, basally feathered hairs lying between long, erect, toothed hairs.

Although spiders of the genus Loxosceles are known from Africa, they are most diverse throughout the Americas. Here seventy-four species are found (58 in Mexico and Central America, 6 in the West Indies, 30 in South America). Loxosceles laeta (fig. 4.4c) is a large species. It has gained notoriety because of its tendency to live in urban settings, because it has been introduced into new areas of the world by commerce, and because of its reputation for being especially toxic. As a result, its biology has been studied in some detail (e.g., Galiano 1967, Schenone et al. 1970, Lowrie 1980). Complete bibliographies on violin spider biology and taxonomy are available (Gertsch 1967, Gertsch and Ennik 1983).

References

Bücherl, W. 1961. Aranhas do género Loxosceles e loxoscelismo na América. Cien. Cult. 13: 213-224. Galiano, M. E. 1967. Ciclo biológico y desarollo de Loxosceles laeta (Nicolet, 1849) (Araneae, Scytodidae). Acta Zool. Lilloana 23: 431-464. Gertsch, W. J. f967. The spider genus Loxosceles in South America (Araneae, Scytodidae). Amer. Mus. Nat. Hist. Bull. Í36: f 17-174. Gertsch, W. J., and F. Ennik. 1983. The spider genus Loxosceles in North America, Central America, and the West Indies (Araneae, Loxoscelidae). Amer. Mus. Nat. Hist. Bull. 175: 264-360. Lowrie, D. C. 1980. Starvation longevity in Loxosceles laeta (Nicolet) (Araneae). Entoniol. News 91: 130-132. Schenone, H., A. Rojas, and H. Reyes. 1970. Prevalence of Loxosceles laeta in houses in central Chile. Amer. J. Trop. Med. Hyg. 19: 564-567.

Schenone, H., and G. Suárez. 1978. Venoms of Scytodidae, genus Loxosceles. In S. Bettini, ed., Arthropod venoms. Springer, Berlin. Pp. 247-275.

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