Spiders

Arachnida, Araneae (= Araneida). Spanish: Aranas. Portuguese: Aranhas. Quechua: Vilca-kuna. Tupi-Guarani: Nhandui. Nahuatl: Tocameh, sing, tocatl (Mexico).

Spiders (Foelix 1982, Gertsch 1979, Pre-ston-Mafham and Preston-Mafham 1984) comprise a large and very familiar group and are fascinating and diverse in Latin America (Robinson 1984). The abdomen is almost always unsegmented and narrowly attached to the cephalothorax by a stalk. The chelicerae are modified into fangs connected to internal poison glands.

The pedipalps are leglike, and there are short terminal abdominal appendages developed in association with silk glands that open between them (spinnerets).

These creatures are found in all natural situations, often in close association with humans (Turnbull 1973). Most are reclusive and select dark retreats as living quarters. They are often found in caves (Gertsch 1973, Brignoli 1972). Others, however, are sun loving and free ranging. Several kinds even inhabit the marine intertidal zone (Roth and Brown 1975). In seasonal climates, they may be most abundant in wet periods when more prey is available than during dry periods (Lubin 1978).

Although spiders are typically solitary, a number of species show extended parental care and even relatively permanent social gatherings (Burgess 1978, Buskirk 1981). In a few species, colony members even cooperate in web building and nest maintenance, displaying mutual tolerance and communication (Buskirk 1981, Lubin 1980).

Since pre-Columbian times, people in Central Mexico have brought branches with the webs and spiders of a small (BL 5 mm) social species, called el mosquero (Mallos gregalis), into their homes to reduce the number of flies that invade during the rainy season (Simon 1909). Many individuals cooperate to build a dense sheet web with many chambers and retreats. They not only exhibit group tolerance but practice communal prey capture as well (Burgess 1979, but see Jackson 1979 and Tietjen 1986). The nest is occupied and expanded by successive generations (Burgess 1976). The theridiid Anelosimus eximius is the most widespread of several communal species in the genus in South America (Rypstra and Tirey 1989). It builds giant webs (1 m by nearly 5 m or more) containing hundreds, even thousands, of individuals who work, prey (Krafft and Pasquet 1991), and spin together (Levi 1963).

The perception and production of sound is developed in many spiders (Le-gendre 1963) but is only one of their many ineans of communication (Witt and Rovner 1982). They also keep in touch by tugging and vibrating the web and through phero-mones and, more rarely, vision.

Many spiders are cryptic in form, color, and behavior, and a considerable number exhibit mimicry, primarily of ants (Peck-ham 1889). They possess structural (elongate body and legs, constricted abdomen), behavioral (forelegs held in elevated position like antennae), and color modifications, all giving them a close resemblance to their formicine models. In the Neo-tropics, these mimics mostly belong to the families Clubionidae, subfamily Castia-neirinae (Reiskind 1969), such as Castia-neira rica (Reiskind 1970, 1977), and Salticidae (see Jumping Spiders, below). Some species even resemble several distinct types of ants through variation in colors, sexual dimorphism, and changes during development, so-called transformational mimicry. Velvet ants (Mutillidae) are also mimicked.

Several kinds of small flies are associated with spiders, as commensals (Robinson and Robinson 1977) or by using the web as protected perches (Lahmann and Zúñiga

1981). Symbioses involving spiders seem rare, although a few unstudied cases of interactions with ants are known (Noonan

1982). There are many kleptoparasitic types that live in the webs of other species from which they steal unattended prey (arañas ladronas, Restrepo 1948).

All spiders are obligate carnivores and possess venom produced by large internal glands that empty their products through ducts opening at the tips of the fangs. Spiders use poison to subdue prey or in defense. The quantity of venom and toxicity of most is slight, so that spider bites are usually of little or no medical importance. A few species, however, do have the capacity of harming (Bettini and Brignoli 1978, Schenone 1953) or even killing humans.

Some of these are found in Latin America, mainly in the genera Trechona, Phoneutria, and Latrodectus, whose venoms are neurotoxic. Loxosceles bites, containing hemolytic toxins, while occasionally severely disfiguring, are not lethal (Biicherl 1971).

Although other arthropods spin silk, nowhere is the process so well developed and web making so elaborate as in the spiders (Savory 1952). Spider silk has the highest tensile strength of any natural fiber and is ideal for constructing snares and traps for insects, as well as nests, retreats, and other structures. Webs may be relatively small, amorphous, and loosely formed or highly complex, symmetrical, and large, as in the orb weavers. The relative abundance of the different types depends on the taxonomic composition and ecological characteristics of an area (Lieberman-Jaffe 1981).

The number of species forming the Neotropical spider fauna is unknown but must be very large. There are few general works for the region (Pikelin and Schi-apelli 1963). Two major groups are recognized, the Labidognatha (most), in which the chelicerae, or fangs, work laterally, like pliers against each other, and the Orthognathia, in which the fangs are parallel and fold back along the long axis of the body (tarantulas and relatives).

Most spiders have eight "eyes" located on the back of the anterior portion of the céphalothorax. The number and arrangement relative to these eyes are often used as identifying characteristics.

References

Bettini, S., and S. M. Brignoli. 1978. Review of the spider families, with notes on the lesser-known poisonous forms. In S. Bettini, ed., Arthropod venoms. Springer, Berlin. Pp. 101-120.

Brignoli, P. M. 1972. Sur quelques araignés cavernicoles d'Argentine, Uruguay, Brésil et Vénézuela récoltées par le Dr. P. Strinate (Arachnida, Araneae). Rev. Suisse Zool. 79: 361-385.

Bücherl, W. 1971. Spiders. In W. Bücherl and E. E. Buckley, eds., Venomous animals and their venoms. 3. Venomous invertebrates. Academic, New York. Pp. 197-277.

Burgess, J. W. 1976. Social spiders. Nat. Hist. 234:101-106.

Burgess, J. W. 1978. Social behavior in group-living spider species. Zool. Soc. London Symp. 42: 69-78.

Burgess, J. W. 1979. Web-signal processing for tolerance and group prédation in the social spider Mallos gregalis. Simon. J. Anim. Behav. 27: 157-164.

Buskirk, R. E. 1981. Sociality in the Arachnida. In H. R. Hermann, ed., Social insects. 2: 281-367. Academic, New York.

Foelix, R. F. 1982. Biology of spiders. Harvard Univ. Press, Cambridge.

Gertsch, W. J. 1973. A report on cave spiders from Mexico and Central America. Assoc. Mex. Cave Stud. Bull. 5: 141-163.

Gertsch, W.J. 1979. American spiders. 2d ed. Van Nostrand Reinhold, New York.

Jackson, R. R. 1979. Predatory behavior of the social spider Mallos gregalis: Is it cooperative? Ins. Soc. 26: 300-312.'

Krafft, B., and A. Pasquet. 1991. Synchronized and rhythmical activity during the prey capture in the social spider Anelosimus eximius (Araneae, Theridiidae). Ins. Soc. 38: 83-90.

Lahmann, E. J., and C. M. Züniga. 1981. Use of spider threads as resting places by tropical insects. J. Arachnol. 9: 339-341.

Legf.ndre, R. 1963. L'audition et 1'emission de sons chez les aranéides. Ann. Biol. Ser. 4(2): 371-390.

Levi, H. W. 1963. The American spiders of the genus Anelosimus (Araneae: Theridiidae). Amer. Micro. Soc. Trans. 82: 30-48.

Lieberman-Jaffe, S. 1981. Ecology of web-building spiders at Corcovado National Park, Costa Rica: A preliminary study. Stud. Neotrop. Fauna Environ. 16: 99-106.

Lubin, Y. D. 1978. Seasonal abundance and diversity of web-building spiders in relation to habitat structure on Barro Colorado Island, Panama. J. Arach. 6: 31-51.

Lubin, Y. D. 1980. Population studies of two colonial orb-weaving spiders. Zool. J. Lin-naean Soc. 70: 265-287.

Noonan, G. R. 1982. Notes on interactions between the spider Eilica puno (Gnaphosidea) and the ant Camponotus inca in the Peruvian Andes. Biotropica 14: 145-148.

Peckham, G. W. 1889. Protective resemblances in spiders. Nat. Hist. Soc. Wise. Occ. Pap. 1: 61-113.

PlKF.lln, B. s. G., and R. D. schiapelli. 1963. Llave para la determinación de familias de arañas argentinas. Physis 24: 43—72.

Prf.ston-Mafham, R., and K. Preston-Maf-ham. 1984. Spiders of the world. Facts on File, New York.

Reiskind, J. 1969. The spider subfamily Casti-aneirinae of North and Central America. Mus. Comp. Zool. (Harvard Univ.) Bull. 138-163-325.

Reiskind, J. 1970. Multiple mimetic forms in an ant-mimicking clubionid spider. Science 169-587-588.

Reiskind, J. 1977. Ant-mimicry in Panamanian clubionid and salticid spiders (Araneae: Clubionidae, Salticidae). Biotropica 9: 1-8.

Restrepo, A. 1948. La araña ladrona. Fac. Nac. Agron. (Medellin) Rev. 17: 157-168.

Robinson, M. H. 1984. Neotropical arach-nology: Historic, ecological and evolutionary aspects. 9th Cong. Latinoamer. Zool. (Arequipa) Inf. Final. Pp. 89-100.

Robinson, M. H., and B. Robinson. 1977. Association between flies and spiders: Bibio-commensalism and dipsoparasitism. Psyche 84: 150-157.

Roth, V. D., and W. L. Brown. 1975. A new genus of Mexican intertidal zone spider (Desidae) with biological and behavioral notes. Amer. Mus. Nov. 2568: 1-7.

Rypstra, A. L., and R. S. Tirey. 1989. Observations on the social spider, Anelosimus domingo (Araneae, Theridiidae), in southwestern Peru. J. Arachnol. 17: 368-370.

Savory, T. H. 1952. The spider's web. Warne, London.

Schenone, H. 1953. Mordeduras de arañas. Bol. Chileno Parasit. 8: 35-37.

Simon, E. 1909. Sur l'araignée Mosquero. Acad. Sei. (Paris) Compt. Rend. Séance 148: 736-737.

Tietjen, W. J. 1986. Social spider webs, with special reference to the web of Mallos gregalis. In W. A. Shear, ed., Spiders: Webs, behavior, and evolution. Stanford Univ. Press, Stanford. Pp. 172-206.

Turnbull, A. L. 1973. Ecology of the true spiders (Araneomorphae). Ann. Rev. Entomol. 18: 305-348.

Witt, P. M., and J. S. Rovner, eds. 1982. Spider communication: Mechanisms and ecological significance. Princeton Univ. Press, Princeton.

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