Overview

Brief Summary

The Australian redback spider (Latrodectus hasselti) is one of the widow spiders (Latrodectus), a cosmopolitan group of small, round-bodied spiders. Although its native range is presumed to be Australia, L. hasselti has been inadvertently introduced to New Zealand, Japan, Southeast Asia, and possibly elsewhere (Garb et al. 2004 and references therein). The New Zealand endemic Latrodectus katipo appears to be the closest extant relative to L. hasselti. The phylogeny and biogeography of the genus Latrodectus have been reviewed by Garb et al. (2004).

Female redback spiders are black (occasionally brownish) with an obvious orange to red longitudinal stripe on the upper abdomen, with the red stripe sometimes being broken, and an hourglass-shaped red/orange spot on the underside of the abdomen. Females are about a centimeter long, but males are just a few millimeters. The males' red markings are often less distinct. The male's body is light brown with white markings on the upper side of the abdomen and a pale hourglass marking on the underside. Juveniles have additional white markings on the abdomen (http://australianmuseum.net.au/Redback-Spider, accessed 24 December 2009)

Latrodectus hasselti is well known for its sexual cannibalism. Females often consume males during copulation following the stereotyped self-sacrifice ‘‘somersault’’ behavior performed by the male (Forster 1992; Andrade and Banta 2002). After insertion of  one of his copulatory organs (palps), the male turns a somersault through 180 degrees so that his abdomen comes to rest against the female's mouthparts, whereupon she may begin to devour him (Forster 1992). The cannibalistic process is slow and males may use their two palps to copulate sequentially with a single female--inseminating one of her two independent sperm storage organs with each palp--then sacrifice themselves to their cannibalistic mates. This extreme strategy increases paternity for the mating in question, but also results in the male's death, eliminating the possibility of copulating with additional females (Andrade 1996; Andrade and Banta 2002). Andrade et al. (2005) documented a novel male trait—an abdominal constriction that appears during courtship—that allows a male to survive partial cannibalism from the first copulation and go on to mate with a female a second time. Inseminating both of the female's sperm storage organs by copulating with her twice dramatically increases the male's paternity share in the event the female proceeds to mate with additional males. This constriction allows males to overcome the potential fitness limit imposed by their own suicidal strategy by prolonging survival across two cannibalistic copulations.

A female may mate sequentially with different males and under some circumstances may choose to reduce the paternity share of one of the males by consuming him sooner rather than later (Stoltz et al. 2009).

As is true for other Latrodectus, during Latrodectus hasselti copulation, a discrete portion of the male's copulatory organ (the apical sclerite) breaks off and remains in the female's reproductive tract (Andrade 1996; Snow et al. 2006). This broken off apical sclerite reduces sperm competition from other males subsequently mating with the same female by acting as a "sperm plug", physically blocking access to the female's sperm storage organ (Snow et al. 2006).

Latrodectus hasselti is among the most medically significant spiders in the world. Humans are bitten far more often by females than by the smaller males. The bite often causes severe pain and other symptoms lasting for days (Isbister and Gray 2003). A variety of Latrodectus widow spider species are found around the world and their bites tend to produce similar symptoms. Bites are often followed by  the gradual onset of severe, unremitting local, regional, and systemic symptoms. These may include pain at the bite site or in the whole of the bitten limb, intense sweating, piloerection ("goosebumps"), and muscle fasciculations (twitching). Symptoms may become severe and generalized and include hypertension (elevated blood pressure), tachycardia (abnormally rapid heartbeat), nausea, vomiting, and abdominal pain. Although death is extremely uncommon, patients may be left with serious symptoms for days or weeks if left untreated (Graudins et al. 2001). There is an effective antivenom treatment for L. hasselti bites and several studies have found this antivenom to be effective in treating bites from other Latrodectus species as well (Gaudins et al. 2001). According to Wiener (2003), there have been no deaths from L. hasselti bites since antivenom became available in 1956.

  • Andrade, M. C. B. (1996). Sexual Selection for Male Sacrifice in the Australian Redback Spider. Science. 271, 70-72.
  • Andrade, M. C. B., & Banta E. M. (2002). Value of male remating and functional sterility in redback spiders. Animal Behaviour. 63, 857-870.
  • Andrade, M. C. B., Gu L., & Stoltz J. A. (2005). Novel male trait prolongs survival in suicidal mating. Biology Letters. 1, 276-279.
  • Forster, L. M. (1992). The Stereotyped Behaviour of Sexual Cannibalism in Latrodectus hasselti Thorell (Araneae : Theridiidae), the Australian Redback Spider. Australian Journal of Zoology. 40, 1-11.
  • Garb, J. E., Gonzalez A., & Gillespie R. G. (2004). The black widow spider genus Latrodectus (Araneae: Theridiidae): phylogeny, biogeography, and invasion history. Molecular Phylogenetics and Evolution. 31, 1127-1142.
  • Graudins, A., Padula M., Broady K., & Nicholson G. (2001). Red-Back Spider (Latrodectus hasselti) Antivenom Prevents the Toxicity of Widow Spider Venoms. Annals of Emergency Medicine. 37, 154-160.
  • Isbister, G. K., & Gray M. R. (2003). Latrodectism: a prospective cohort study of bites by formally identified redback spiders. Medical Journal of Australia. 179, 88-91.
  • Snow, L. S. E., Abdel-Mesih A., & Andrade M. C. B. (2006). Broken Copulatory Organs are Low-Cost Adaptations to Sperm Competition in Redback Spiders. Ethology. 112, 379-389.
  • Stoltz, J. A., Elias D. O., & Andrade M. C. B. (2009). Male courtship effort determines female response to competing rivals in redback spiders. Animal Behaviour. 77, 79-85.
  • Wiener, S. (2003). Latrodectism: a prospective cohort study of bites by formally identified redback spiders [letter]. Medical Journal of Australia. 179, 455.
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Taxon Biology

The Australian redback spider (Latrodectus hasselti) is one of the widow spiders (Latrodectus), a cosmopolitan group of small, round-bodied spiders.

Female redback spiders are black (occasionally brownish) with an obvious orange to red longitudinal stripe on the upper abdomen, with the red stripe sometimes being broken, and an hourglass-shaped red/orange spot on the underside of the abdomen. Females are about a centimeter long, but males are just a few mm. The males' red markings are often less distinct. The male's body is light brown with white markings on the upper side of the abdomen and a pale hourglass marking on the underside. Juveniles have additional white markings on the abdomen (http://australianmuseum.net.au/Redback-Spider, accessed 24 December 2009)

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Distribution

Redback spiders are native to all areas of Australia. Redbacks are also found in New Zealand (North and South islands), having been introduced through grape importation from Australia. Records of the spiders’ appearance span most of Southeast Asia, including as far north as India. This species has also recently been sighted in south central Japan.

Biogeographic Regions: oriental (Introduced ); australian (Native ); oceanic islands (Introduced )

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Although its native range is presumed to be Australia, Latrodectus hasselti has been inadvertently introduced to New Zealand, Japan, Southeast Asia, and possibly elsewhere (Garb et al. 2004 and references therein).

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Physical Description

Morphology

Redback spiders are bilaterally symmetrical, cold-blooded spiders belonging to the family Theridiidae. Their closest relative is the North American southern black widow spider (Latrodectus mactans), which is distinguishable from redback spiders by the absence of a red dorsal stripe. Female redbacks average 10 mm in length, with body sizes as large as a pea, and are significantly larger than males (which average 3-4 mm). Females are typically black with a red stripe, sometimes broken, on the dorsal surface of the upper abdomen (crossing parallel to the length of the body), and a red hourglass-shaped spot on the ventral side of the abdomen. Young female redbacks have additional white markings on their abdomens that they lose as adults. Male redbacks are typically light brown in color with a dorsal red stripe and a paler hourglass shape on the ventral side of the abdomen, both of which are similar to, but less distinct than, female markings. Males also retain the white markings on the upper side of the abdomen through adulthood. Each sex has slender legs and is venomous.

Range length: 3 to 10 mm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; venomous

Sexual Dimorphism: female larger; sexes colored or patterned differently; female more colorful

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Ecology

Habitat

Redback spiders are most commonly found in urban areas, preferring the shelter human habitats provide from unfavorable weather. They inhabit urban and suburban areas within all of Australia's terrestrial biomes, preferring tropical and temperate areas. They are less common in savanna, chaparral and desert areas and are not found at the continent's highest elevations. The appearance of redbacks in Japan shows that they are also capable of surviving at very low temperatures (-3 degrees C).

Range elevation: 0 (low) m.

Habitat Regions: temperate ; tropical ; terrestrial

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; rainforest

Other Habitat Features: urban ; suburban

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Trophic Strategy

Redback spiders are insectivores that prey on small insects caught within their webs such as ants (Formicidae spp). They also sometimes catch larger animals stuck in their webs such as mice, small birds, snakes, small lizards, king crickets, Cromwell chafer beetles, and trapdoor spiders. Redback spiders also steal stored prey caught in the webs of other spiders. All redbacks have a potentially venomous bite, however only females have been known to envenomate prey.

Redback spiders catch their prey in a unique way. At night, females construct a complex web system reaching in all directions, including towards the ground. They set traps for prey by bringing a strand of their silk web down and sticking it to the ground surface. Next, they climb up that line, adding an additional silk line on top of the original to strengthen it. They then pull the line taut and a single trap is complete. They do this multiple times creating a number of traps and wait for prey to run or fly into a line and get stuck. Redbacks eventually wrap up each prey item, storing some for later meals.

Animal Foods: birds; mammals; reptiles; insects; terrestrial non-insect arthropods

Foraging Behavior: stores or caches food

Primary Diet: carnivore (Insectivore )

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Associations

The primary ecosystem role of this species is as an insect predator. They can have a negative impact on some arthropod communities as a predator and by displacing other species. Redback spiders were a factor in the endangerment of Cromwell chafer beetles (Prodontria lewisii). They are also prey for a small number of species, including daddy longlegs (Pholcus phalangioides) and white-tailed spiders (Lampona spp). There is evidence that their egg sacs are a target for Philolema latrodecti and Ichneuman wasps (Ichneumonidae).

Ecosystem Impact: creates habitat

Commensal/Parasitic Species:

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Redback spiders are aposematic; their red markings warn predators of their venomous nature. Unsurprisingly then, few species prey on redbacks; only daddy longlegs and white-tailed spiders have been seen to repeatedly catch and kill redbacks. There is also evidence that their eggs are preyed on by Mantisflies (Mantisipidae).

Known Predators:

Anti-predator Adaptations: aposematic

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Life History and Behavior

Behavior

Webs are constructed so that spiders are able to sense vibrations, using their hair-like setae, made by animals running into the web's strands. Unmated female redbacks deposit a chemical pheromone on their webs to attract males and, during courtship, male redbacks must make their presence known using tactile cues to avoid being consumed. As with most spiders, redbacks have simple eyes that are capable of sensing movement.

Communication Channels: visual ; tactile ; chemical

Other Communication Modes: pheromones ; vibrations

Perception Channels: visual ; tactile ; vibrations ; chemical

  • Jerhot, E., J. Stolz, M. Andrade, S. Schulz. 2010. Acylated Serine Derivatives: A Unique Class of Arthropod Pheromones of the Australian Redback Spider, Latrodectus hasselti. Angewandte Chemie - International Edition, 49/11: 2037-2040.
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Behaviour

Latrodectus hasselti is well known for its sexual cannibalism. Females often consume males during copulation following the stereotyped self-sacrifice ‘‘somersault’’ behavior performed by the male (Forster 1992; Andrade and Banta 2002). After insertion of one of his copulatory organs (palps), the male turns a somersault through 180 degrees so that his abdomen comes to rest against the female's mouthparts, whereupon she may begin to devour him (Forster 1992). The cannibalistic process is slow and males may use their two palps to copulate sequentially with a single female--inseminating one of her two independent sperm storage organs with each palp--then sacrifice themselves to their cannibalistic mates. This extreme strategy increases paternity for the mating in question, but also results in the male's death, eliminating the possibility of copulating with additional females (Andrade 1996; Andrade and Banta 2002). Andrade et al. (2005) documented a novel male trait—an abdominal constriction that appears during courtship—that allows a male to survive partial cannibalism from the first copulation and go on to mate with a female a second time. Inseminating both of the female's sperm storage organs by copulating with her twice dramatically increases the male's paternity share in the event the female proceeds to mate with additional males. This constriction allows males to overcome the potential fitness limit imposed by their own suicidal strategy by prolonging survival across two cannibalistic copulations.

A female may mate sequentially with different males and under some circumstances may choose to reduce the paternity share of one of the males by consuming him sooner rather than later (Stoltz et al. 2009).

As is true for other Latrodectus, during Latrodectus hasselti copulation, a discrete portion of the male's copulatory organ (the apical sclerite) breaks off and remains in the female's reproductive tract (Andrade 1996; Snow et al. 2006). This broken off apical sclerite reduces sperm competition from other males subsequently mating with the same female by acting as a "sperm plug", physically blocking access to the female's sperm storage organ (Snow et al. 2006).

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Life Cycle

Young redback spiders follow a similar developmental sequence to other spider species. A week and a half after females lay their egg sacs, the first molt occurs inside individual eggs. The first instar (stage between molts) follows, during which spiderlings hatch and disperse within 14 days, usually via wind currents. Young spiders look like small adults. Members of this species reach maturity and adult size after 4 instars/5 molts (males) or 6 instars/7 molts (females).

  • Commonwealth Scientific and Industrial Research Organization (CSIRO). 2012. "Redback spider" (On-line). Commonwealth Scientific and Industrial Research Organization (CSIRO). Accessed September 08, 2012 at http://www.csiro.au/Outcomes/Environment/Biodiversity/Redback-Spiders.aspx.
  • Downes, M. 1987. Postembryonic Development of Latrodectus hasselti Thorell (Araneae, Theridiidae). Journal of Arachnology, 14: 293-301.
  • Hickman, C., L. Roberts, S. Keen, A. Larson, D. Eisenhour. 2007. Animal Diversity - Fifth Edition. New York, New York: McGraw-Hill.
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Life Expectancy

Female Redback spiders live for 2-3 years whereas males only live for about 6-7 months. Male lifespan is limited by sexual cannibalism during mating, male-male competition, and size differential between males and females (often leading to females killing the much smaller males).

The presence of Redback spider populations in Japan shows that they are capable of surviving without food for long periods of time, as they likely traveled the long distance from Australia to Japan in cargo carried by ships with little to no food available. Juveniles may survive up to 160 days and adults 300 days without food. At later stages of starvation they are sluggish and incapable of finding food for themselves, however Redbacks are noted to recover immediately after one meal.

Typical lifespan

Status: wild:
6 to 36 months.

  • Forster, L., J. Kavale. 1989. Effects of food deprivation on Latrodectus hasselti Thorell (Araneae: Theridiidae), the Australian redback spider. New Zealand Journal of Zoology, 16: 401-408.
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Reproduction

Redback spiders can mate anytime during the year but do so most commonly during summer months when temperatures are higher. Redback spiders are polyandrous (males typically mate once while females often have multiple mates). This species' mating behavior includes sexual cannibalism. Smaller males attempt to mate multiple times with a single, much larger, female. When they approach a female, a male will insert one pedipalp into one of the female's sperm-storage organs. During this action it will twist its body 180 degrees, placing its abdomen directly near the female's fangs (a "copulatory somersault"). Early in this first sperm transfer, the female begins to masticate her partner; most males (69.6-83.3%), are able to break free of this first restraint. After additional courtship behaviors by males, the mating behavior described is repeated, with the male's second pedipalp inserted into the female's other sperm-storage organ. Following 65% of these second insertions, the female will completely consume the male.

Some male redbacks have adapted a unique behavior called "mid-dorsal abdominal constriction" in order to increase survival after the first attempt of female cannibalism. This involves manually shrinking their abdomens and, in so doing, shifting essential organs anteriorly, lengthening survival time of males so they may inseminate the female’s second sperm-storage organ. Those who succeed at this behavior increase chances of paternity.

Due to cannibalistic behaviors by females, a majority of male redbacks only mate with one female. During the mating period, several males are typically found on a female's web, leading males to compete with one another, often fatally, for access to females. Redbacks have a lengthy courtship period of around 3 hours; however, males may rush these activities if another male is detected approaching. If they attempt to shorten courtship too much, females typically cannibalize males before copulation is completed. During copulation, the apical sclerite of the male redback spider's copulatory organ may break off and act as a plug in the female's sperm-storage organs, blocking insemination by other males and helping increase chances of paternity for the first mate. Cannibalized males who exhibit this behavior potentially more than double their likelihood of paternity compared to males not consumed. After consumption of a male, females are much less receptive to further mates. Because 80% of males never find a mate, it is important to invest everything into their one mating experience. Redback spider males who survive copulation are likely sterile for the rest of their lives.

Mating System: polyandrous

Redback spiders in Australia can breed at any time of year, but breeding is most common during summer months. After females have mated, they may use internally stored sperm for up to 2 years to fertilize their eggs. During this time they lay multiple batches of eggs, from different supplies of sperm, with a period of at least 1-3 weeks between each batch. Batches are made up of about 10 egg sacs, each of which contains approximately 250 eggs, which are laid and suspended in the web. When sacs are laid they are white but after time turn brown. The length of time before hatching is related to temperature. It has been recorded that they emerge after 17-24 days at 30°C and after 26-43 days at 25°C. The average duration of egg to spiderling emergence is 28.7 days. Below 25°C, development is typically arrested. Once emerged, sexual organs start soon begin developing, with female redback spiders reaching sexual maturity after 120 days and the males after 90 days.

Breeding interval: Redback spiders are capable of breeding once every 1-3 weeks.

Breeding season: Year round (most common during summer months)

Average number of offspring: 2500.

Range gestation period: 17 to 43 days.

Average gestation period: 28.7 days.

Average age at sexual or reproductive maturity (female): 120 days.

Average age at sexual or reproductive maturity (male): 90 days.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); oviparous ; sperm-storing ; delayed fertilization

Information on parental investment for this species is limited. Females lay large numbers of eggs and suspend them in bundles from their webs, possibly as a form of protection. When hatched, spiderlings quickly disperse from their mother's territory. Because male redbacks typically do not survive past mating, it is assumed that no male parental investment occurs.

Parental Investment: female parental care ; pre-hatching/birth (Protecting: Female)

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Evolution and Systematics

Evolution

Systematics and Taxonomy

The phylogeny and biogeography of the genus Latrodectus have been reviewed by Garb et al. (2004).

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Sister Taxon

The New Zealand endemic Latrodectus katipo appears to be the closest extant relative to L. hasselti (Garb et al. 2004).

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Latrodectus hasselti

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1
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Barcode data: Latrodectus hasseltii

The following is a representative barcode sequence, the centroid of all available sequences for this species.


There are 9 barcode sequences available from BOLD and GenBank.

Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.

See the BOLD taxonomy browser for more complete information about this specimen and other sequences.

C-I---------------------------------------------------TTGATTTTTGGGGCTTGGGCAGCTATAGTTGGGACAGCAATA---AGAGTATTAATTCGTACTGAGTTAGGACAACCTGGTAGATTGTTAGGTGAC---GACCAGTTATATAATGTAATTGTAACAGGGCATGCTTTTGTTATAATTTTTTTTATAGTAATGCCTATTTTGATTGGAGGGTTTGGGAACTGATTAGTTCCTCTGATA---TTAGGAGCTCCTGATATGGCTTTCCCTCGAATAAATAATTTAAGATTTTGACTTTTACCTTCATCATTGATTTTATTGTTTATTTCTTCTTTAGAGGAAGTAGGGGTTGGGGCAGGATGAACAATCTACCCGCCTTTGTCAAGATTAGAGGGTCATAGAGGGAGATCTGTGGATTTT---GCTATTTTTTCCTTGCATTTGGCAGGTGCTTCTTCTATTATAGGGGCTATTAATTTTATTTCTACTATTTTAAACATACGTTTAGTAGGGGTTTCGATAGAAAAGGTAAGATTATTTGTCTGGTCAGTGTTGATCACTGCGGTATTATTATTGTTATCATTACCTGTTTTAGCTGGT---GCCATTACTATACTACTAACTGATCGTAATTTTAATACTTCATTTTTTGATCCTGCTGGTGGGGGGGACCCCATTTTATTTCAACATTTGTTTTGATTTTTTGGGCACCCTGAGGTTTATATTTTAATTTTGCCTGGATTTGGGATTGTATCTCATGTTATTAGAGCTTCTGTAGGGAAGCGG---GAGCCTTTTGGTAGTTTAGGAATAATTTATGCTATAGTAGGAATTGGAGGGATAGGTTTTGTTGTGTGAGCGCATCATATATTTTCAGTTGGAATGGATGTGGATACCCGGGCATATTTTACTGCTGCTACTATAATTATTGCAGTGCCGACAGGTATTAAGGTCTTTAGATGGATA---GCTACT
-- end --

Download FASTA File

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Statistics of barcoding coverage: Latrodectus hasseltii

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 7
Specimens with Barcodes: 7
Species With Barcodes: 1
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Conservation

Conservation Status

Redback spiders do not currently have any special conservation status.

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Latrodectus hasselti has been expanding its range for many years via inadvertent introductions to new regions by human activity and its conservation status is not a concern. However, its introduced range now includes New Zealand and there is some concern that this species could threaten the endemic New Zealand widow spider L. katipo via asymmetric hybridization and genetic swamping (Garb et al. 2004 and references therein).

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Relevance to Humans and Ecosystems

Benefits

Redback spiders are one of the most dangerous spiders in Australia. When disturbed, larger females often bite and envenomate intruders. Bites typically occur during the summer season and in the late afternoon when temperatures are highest and the spiders are most active. The venom is produced in the cephalothorax and is delivered via the animal's fangs. Redback spiders can control the amount of venom that they inject and "dry" bites are not unheard of. The main toxic component of the venom, α-latrotoxin, affects humans differently depending on the amount injected. Males are believed to be as capable of delivering painful, venomous bites as females, although bites are rarely reported. Approximately 80% of bites cause little to no effect. Of the remaining 20%, most feel pain radiating from the bite spot for only about 24 hours. More serious cases include pain lasting longer than 24 hours, bumps and swollen lymph nodes followed by sweating, a rapid heart beat, possible vomiting, headache, and insomnia. Unlike most other envenomation syndromes, the effects of bites from this species may persist for several days, weeks, or months. Fatalities from redback bites are rare and none have occurred since 1956, when an antivenom was created. Most bites from this species can be treated with household remedies (ice packs and pain relievers). Bites that show more severe symptoms may require antivenom to be administered intramuscularly, sometimes in multiple injections. Recently, Australian doctors have chosen to only give the antivenom when absolutely necessary because they fear possible negative side effects. Other doctors are not convinced of its effectiveness in general.

Negative Impacts: injures humans (bites or stings, venomous )

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While redback spiders are predators of terrestrial insects, they do not appear to affect insect populations enough to have any positive effects on humans.

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Risks

Risk Statement

Latrodectus hasselti is among the most medically significant spiders in the world. Humans are bitten far more often by females than by the smaller males. The bite often causes severe pain and other symptoms lasting for days (Isbister and Gray 2003). A variety of Latrodectus widow spider species are found around the world and their bites tend to produce similar symptoms. Bites are often followed by the gradual onset of severe, unremitting local, regional, and systemic symptoms. These may include pain at the bite site or in the whole of the bitten limb, intense sweating, piloerection ("goosebumps"), and muscle fasciculations (twitching). Symptoms may become severe and generalized and include hypertension (elevated blood pressure), tachycardia (abnormally rapid heartbeat), nausea, vomiting, and abdominal pain. Although death is extremely uncommon, patients may be left with serious symptoms for days or weeks if left untreated (Graudins et al. 2001). There is an effective antivenom treatment for L. hasselti bites and several studies have found this antivenom to be effective in treating bites from other Latrodectus species as well (Gaudins et al. 2001). According to Wiener (2003), there have been no deaths from L. hasselti bites since antivenom became available in 1956.

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© Shapiro, Leo

Source: EOL Rapid Response Team

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