Elassoctenus Harpax Of Austraila Medical Importance

Approximately 3,000 genera and 36,000 species of spiders have been described worldwide. In North America alone there are 64 families, some 500 genera, and 3,400 species (Coddington et al., 1990). Among the more than 100 families of spiders, about 20 families include species that reportedly cause medical concerns when they bite humans and other animals. The 5 most important families are the Dipluridae, Hexathelidae, Theraphosidae, Sicari-idae (Loxoscelidae), and Theridiidae. See Bettini and Brignoli (1978) and Ori (1984) for additional venomous spiders representing more than 60 genera worldwide.

The order Araneae is divided into two suborders: the Mesothelae and Opisthothelae. The Mesothelae include the single family Liphistiidae, a small group of primitive spiders in Southeast Asia and the Indo-Malaysian region. The Opisthothelae are composed of two groups: the Mygalomorphae (tarantula-like spiders) and Araneomorphae (all other spiders). The mygalomorphs are the more primitive spiders, represented by trap-door spiders, funnel-web spiders, and tarantulas. They include the largest spiders. The araneomorphs are a very diverse group that include wandering spiders and those which are familiar to most people by the diversity of silken webs which they produce.

Taxonomic catalogs of the world spider fauna are provided by Roewer (1942-1954), Bonnet (1945-1961), Brignoli (1983), and Platnick (1989,1993). For identification keys to the families and genera of mygalomorphs, see Raven (1985), and for North American families and genera of spiders, see Kaston (1978) and Roth (1993).

The following is a synopsis of the major families of medical-veterinary importance.

This small group is closely related to the typical trap-door spiders of the family Ctenizidae, which they resemble both morphologically and behaviorally. They construct vertical, silk-lined burrows in the soil, the opening at the surface of which is covered by a hinged "trap door." Their venom is weakly neurotoxic to vertebrates and causes no necrosis. Of the three recognized genera, only Actinopus in Central and South America has been reported as biting humans, producing only local pain and transient muscle contractions.

Members of this family are closely related to the Theraphosidae, or tarantulas, and are largely restricted to southern Africa and Australia. Idiommata blackwelli occurs widely throughout Australia in dry areas, where it constructs silk-lined burrows provided with a saucer-shaped door that fits tightly into the opening at the ground surface. Its bite is painful, causing local redness and edema in humans. Most encounters occur when wandering males enter homes during the late summer and early fall or when individuals are dislodged from their burrows in new suburban areas when people rake their yards.


Known as sheet-web or funnel-web—building tarantulas, diplurids construct burrows in the ground in a wide range of habitats. The family includes 19 genera. They are particularly abundant in the Southern Hemisphere and Australian region. The venom of Trechona species is especially toxic to humans and has been reported to cause human deaths in South America. Two species of particular importance are Trechona venosa and T. zebra, which occur in tropical forests and coastal areas, where they are encountered on vegetation and along trails. They are very aggressive and, if disturbed, will readily bite. The hexathe-lid genera Atrax, Hadronyche, and Macrothele were previously included in this family.


Formerly included in the Dipluridae, some of the members of this family are regarded as among the most venomous of spiders for humans. Among the 11 recognized genera, Atrax, Hadronyche, and Macrothele are the most dangerous. They are known as funnel-web spiders due to their habit of building expansive, funnel-like webs near the entrance to their shallow, silk-lined burrows in the ground, among rocks, or in stumps and rot holes of trees. The most serious bites are caused by Atrax robustus and Hadronyche formidabilis in Australia.


This is the largest mygalomorph family, with 84 recognized genera. They are best known for their large size and hairy appearance and are familiar to most people as tarantulas. As a group they are primarily tropical and subtropical, occurring widely throughout both the Old World and New World, where they are variously known as bird spiders, bird-eating spiders, and monkey or baboon spiders. In North America they extend into the southwestern United States but do not naturally occur east of the Mississippi River. Although the bite of most species is relatively harmless, several genera can cause severe envenomation, particularly in South America, where the genera dangerous to humans are Acanthoscurria, Pamphobeteus, Phormictopus, and Sericopelma. On the Indian subcontinent, the genus Poecilotheria has venom which causes a reaction similar to widow venom, perhaps making it the most dangerous tarantula.

Araneomorph Spiders Agelenidae

Agelenid spiders are called funnel weavers, not to be confused with the mygalomorph funnel-web spiders (Dipluridae and Hexathelidae). They typically build

Mygalomorph Spiders


Barychelidae horizontal sheet webs with a tubular retreat or "funnel" leading into a protected recess. When their webs are constructed in vegetation, they are often called grass spiders. A few species occur in homes, especially in basements and cellars, where their chances of encounters with humans are greatest. The only recognized species of medical concern in North America is the hobo spider, Tegenaria agrestis. In Europe, Agelena labyrinthica and Coelotes obesus have been reported to bite humans.

This is one of the largest families of spiders; it is familiar to most people because of the symmetrical spirallike webs which they construct for snaring flying insects. Known as orb weavers, they are commonly found around homes and other dwellings, where they take advantage of artificial lights to attract prey at night. They seldom bite humans or other vertebrates and usually cause only minor, temporary discomfort when they do. Even the North American black and yellow garden spider, Argiope aurantia, produces only localized pain, redness, and edema on the rare occasions in which it has been known to bite. This is a large and colorful species which often attracts the attention of homeowners in the late summer and fall. A. lobata in Europe causes a similar, mild reaction. Members of the genus Mastophora, known as bolas spiders, possess the most potent venoms among araneid spiders and can cause serious medical problems. Their bites can result in generalized pain and swelling, fever, sweating, hemolysis, and necrosis at the bite site; convulsions and deaths have been reported in some cases. Included in this genus are the podadoras of Bolivia, Chile, and Peru.

Members of this large, diverse family are known as sac spiders, referring to the silken tubular retreats which they typically make in rolled-up leaves, other ground litter, and under bark and stones. They are nocturnal, vagrant spiders which commonly are found hunting prey on plants. They incidentally enter houses and other buildings. Only members of the genus Cheiracanthium are generally regarded as being venomous enough to warrant medical

This family is closely related to the Clubionidae. It includes Trachelas species (e.g., Trachelas volutus), which have been reported to bite humans in the United States, causing a stinging sensation and localized erythema and swelling.


Members of this family are wandering spiders which do not build webs. Most are of moderate size (1.5—2.5 cm in body length) and occur primarily in ground litter and low vegetation, where they hunt prey. They resemble wolf spiders (Lycosidae) in both their general appearance and behavior. The most venomous taxa of medical concern are members of the South American genus Phoneutria, relatively large species (>3 cm) which can cause severe envenomation. Examples are the banana spider (Phoneutria nigriventer) of South America and Elassoctenus harpax of Western Australia, which reportedly inflict painful bites. A human bite case implicating a Florida false wolf spider (Ctenus captiosus) has been documented in Florida. The bite was described as a needlelike puncture with subsequent swelling about the site, nausea, dizziness, and flulike symptoms that persisted for several days (C. Moore and G. B. Edwards, personal communication).


These wandering spiders are commonly found under stones, in rolled leaves, and in ground debris and are known as ground spiders. The bites of most gnaphosids are relatively harmless. Herpyllus blackwalli and H. eccle-siasticus have been reported to cause moderately severe bites in the United States, usually upon entering homes at night.


Members of this family are similar to gnaphosids in their habitats and behavior. The Australian white-tailed spider (Lampona cylindrata) can cause a painful bite with localized inflammation, intensely cyanotic lesions, blistering, persistent ulcerations, and necrosis at the bite site. It is unclear if the damage is due to the venom itself or to associated bacteria that are introduced with the venom (Sutherland, 1987).


Commonly known as wolf spiders, lycosids represent a highly successful family of hunting spiders which are noted for their relatively large size (up to 4 cm) and hairy appearance. Their posterior median and posterior lateral eyes are greatly enlarged and aid them in capturing prey. Members of the genus Lycosa possess cytotoxic venoms which can cause painful bites, and a few cause necrotic skin lesions. Included in this genus are the so-called tarantulas of Europe, such as Lycosa tarentula of tarantism fame. Although the bites of many wolf spiders are painful, they generally cause only temporary, local discomfort.


Clubionidae attention. Corrinnidae

430 Gary R. Mullen Oxyopidae

Members of this largely tropical and subtropical family are called lynx spiders. They are active hunters which rely on their keen eyesight, speed, and agility to capture prey while climbing in foliage. Although the family is not generally regarded as being medically important, females of the green lynx spider (Peucetia viridans) are known to forcibly expel venom from their fangs as a defensive response, especially when guarding their egg sacs. Droplets can be squirted up to 20 cm and on contact with human eyes can cause impaired vision and moderately severe conjunctivitis (Fink, 1984: Tinkham, 1946)

This family is closely related to the wolf spiders, which they strongly resemble. They occur most frequently near water, where they are adept at moving about on the water surface to capture prey, hence their common name fishing spiders. They are also known as nursery-web spiders because of the habit of females suspending their egg sacs in a protective silken "nursery" in vegetation and guarding the resultant spiderlings until they disperse. Because of their large size (body length up to 4 cm or more) and powerful chelicerae, they can bite if handled, causing local pain and transient swelling. The bite of the European species Dolomedes fimbriatus is reported to cause a reaction similar to that of the agelenid Coelotes obesus.

This is the largest family of spiders, with over 400 genera and over 4000 species widely distributed throughout the world. They are known as jumping spiders because of their habit of stalking and pouncing on prey or jumping to escape when threatened. The anterior median eyes are complex and greatly enlarged, providing them with the keenest vision of all spiders. Some of the larger species can be aggressive and inflict painful bites when handled or pressed against the skin. The venom of at least some species contains cytotoxins that cause necrotic lesions at the puncture site, often being slow to heal. The bite of Phidippus johnsoni can cause a dull, throbbing pain that may persist for a few hours, in addition to swelling, tenderness, and itching that may last for 1 —4 days following the bite (Russell, 1970).

Members of this relatively small family live in silken retreats under stones and bark or in crevices of wood and rocks. They are active nocturnal hunters which may enter homes or construct their retreats in and around human dwellings. Despite their large, well-developed chelicerae, they are not very aggressive, rarely bite, and are not considered to be very venomous. Nonetheless, a few cases of human bites by the European species Segestria florentina reportedly have involved local pain, redness, and swelling and occasionally nausea and vertigo.

Sicariidae (Including the Former Loxoscelidae)

The sicariids are a small group of relatively primitive ara-neomorphs. Included in this family are the recluse spiders in the genus Loxosceles, which cause a severe necrosis. Approximately 50 species of Loxosceles have been described in the Americas and at least 70 worldwide. They are generally similar in appearance and are difficult to recognize from one another by the nonspecialist. They typically are found in ground litter and under bark or stones; a few species occur in caves, and some are decidedly synan-thropic, living in close association with humans. Loxosceles species are primarily tropical but have been introduced to temperate regions of Europe, Africa, the Americas, and Australia. The genus Sicarius has been shown to be also highly toxic in laboratory studies.


Members of this large family are called cobweb weavers or comb-footed spiders. The latter refers to a row of serrated bristles on the hind tarsus which is used to comb the silk from the spinnerets during construction of their irregular webs or wrapping prey. The only genus considered particularly venomous to humans and domestic animals is Latrodectus, which includes the widows or shoe-button spiders. Another genus which is purportedly venomous to humans is Steatoda. Several species in South America, including Steatoda andinus (formerly placed in Lithyphantes) and the well-known cirari of Bolivia, Chile, and Paraguay are said to cause serious enveno-mation (Southcott, 1984). Venom of the Mediterranean species S. paykulliana has been shown to be neurotoxic to guinea pigs but this spider has not been reported to bite humans. The cosmopolitan species S.grossa, known as the false black widow, causes only a local bite reaction with no apparent neurotoxic effects (Maretic and Lebez, 1979).


Members of this family are called crab spiders because of their generally flattened appearance, laterigrade legs, and crablike gait. They usually are cryptically colored and ambush their prey from camouflaged sites such as tree bark and flower heads. As a group they are considered harmless to humans and other animals. Some species of Misu-menoides, however, have been suspected of causing relatively minor bites in humans (Hickin, 1984).




ground and other substrates without building a trapping web typically have only two tarsal claws on each leg. Many of these hunting spiders possess dense tufts of hairs (scopu-lae) directly beneath the pair of claws or along the ventral side of the tarsus and metatarsus. They provide physical adhesion to facilitate climbing on smooth surfaces and grasping prey. The scopulae are especially prominent in tarantulas. Three tarsal claws are characteristic of webbuilding spiders. The single median claw on each leg is used to hold onto silken threads by those spiders that hang suspended in their webs.

The abdomen is connected with the cephalothorax by a narrow pedicel, which provides great flexibility and movement between the two body regions. One or two pairs of slitlike openings to the book lungs, the principal respiratory organs in spiders, are located ventrally on the second and third abdominal segments. The more "primitive" spiders tend to retain two pairs of book lungs, whereas most spiders have only one pair. The second pair of book lungs in some spiders is modified to form tubular tracheae that open via a spiracle or pair of spiracles on the third abdominal segment. Most spiders, however, have only a single spiracle located in front of the spinnerets.

The genital opening of both sexes is located ventrally on the second abdominal segment between the book lungs. In females of the more "advanced" spiders, a scle-rotized copuiatory structure called the epigynum is located just in front of the genital opening and leads to the spermathecae, where sperm is stored after mating. The presence of the epigynum is helpful in distinguishing adult females from immatures and males and in distinguishing species.

Located at the posterior end of the abdomen are the spinnerets, through which silk from several types of internal silk glands is extruded via small spigots. Most spiders have three pairs of spinnerets, the size and relative lengths of which provide useful taxonomic characters. In some groups of araneomorph spiders, a sievelike plate of minute spigots called the cribellum is present in front of the anterior pair of spinnerets. These taxa, called cribellate spiders, also possess a row of specialized setae on the metatarsi of the fourth pair of legs called a calamistrum. The calamistrum is used to comb silk from the cribellum by rhythmic movements of the hind legs. The vast majority of araneomorph spiders lack a cribellum and calamistrum and are referred to as ecribellate spiders.

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