ANIMAL SPECIES:Redback Spider
Redback Spiders are found throughout Australia and are common in disturbed and urban areas.
Alternative Names/s
Red-back SpiderIdentification
Redback spiders (Latrodectus hasselti) belong to the Family Theridiidae, which is found worldwide. The notorious Black Widow Spider (Latrodectus sp) of the United States is a close relative of the Redback Spider, and only differs in appearance by the absence of a red dorsal stripe. Other species of Latrodectus occur in Africa, New Zealand (the Katipo), the Pacific Islands, Europe and North and South America.
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. Juveniles have additional white markings on the abdomen. Females have a body about the size of a large pea and slender legs.
The males' red markings are often less distinct. The body is light brown with white markings on the upper side of the abdomen, and a pale hour-glass marking on the underside.
Size range
1 cm (female); 3 mm - 4 mm (male)Similar Species
Grey House Spider, Cupboard SpiderDistribution
They are found Australia-wide and will live almost anywhere as long as there is adequate food, a sheltered web site and warm enough for breeding. They are especially common in disturbed and urban areas, in association with human habitation.
Habitat
Webs consist of a tangled, funnel-like upper retreat area from which vertical, sticky catching threads run to ground attachments. The Redback Spider favours proximity to human habitation, with webs being built in dry, sheltered sites, such as among rocks, in logs, shrubs, junk-piles, sheds, or toilets. Redback Spiders are less common in winter months.
Behaviour and adaptations
Feeding and Diet
Insects are the usual prey of Redback Spiders, but they are capable of capturing quite large animals, such as male trapdoor spiders, king crickets and small lizards, if they become entangled in the web. Prey-stealing is also common, with large females taking stored food items from others' webs.
Life cycle
Once the female has mated, she can store sperm and use it over a period of up to two years to lay several batches of eggs. She spends much time producing up to ten round egg sacs (1cm diameter), which are white, weathering to brown over time. Each egg sac contains approximately 250 eggs and only one to three weeks need to pass before more eggs can be laid. These sacs are suspended within the web. Sometimes small ichneumonid wasps parasitise them, puncturing each sac with tiny holes. The young spiderlings hatch in two to four weeks. Spiderlings are cannibalistic and will eat unhatched eggs and other spiderlings. The spiderlings disperse by ballooning to another suitable nest site on long silk threads that are caught by air currents.
Females mature on average in about four months. The smaller male matures on average in about 90 days. Females may live for two to three years, whereas males only live for about six or seven months.
Mating and reproduction
Male Redback Spiders do not produce a web, but may be found on the fringe of a female's web, especially during the summer mating season. The male has to make overtures to the female to discover whether she is ready to mate, which can prove fatal if she mistakes him for prey. It has been found that in order to occupy the female's attention during mating, the male spider offers her his abdomen by standing on his head and 'somersaulting' his abdomen towards her mouthparts. The female begins to squirt digestive juices onto the male's abdomen while the first palp is inserted. If he is not too weak, he will manage to withdraw, and then insert the second palp. She will continue to 'digest' his abdomen. Most males do not survive this process, which seems to be unique to Latrodectus hasselti.
Predators, Parasites and Diseases
Daddy-long-legs Spiders and White-tailed Spiders are known to catch and kill Redback Spiders.
Evolutionary Relationships
It was once thought that the Redback Spider, Latrodectus hasselti, was a sub species of the Black Widow Spider but it is now known to be a distinct species.
It has also been suggested by some workers that the Redback may not be native to Australia but have been introduced since European settlement, although it's not clear where they originated.
Recent research on the DNA sequences of all recognized Latrodectus species indicates that the Redback is a distinct species, most closely related to the New Zealand Katipo, and probably an Australian native.
Redbacks have most likely become much more common since European settlers started providing them with lots of the kinds of places they like to make webs in.
Living with us
Danger to humans and first aid
Redback bites occur frequently, particularly over the summer months. More than 250 cases receive antivenom each year, with several milder envenomations probably going unreported. Only the female bite is dangerous. They can cause serious illness and have caused deaths. However, since Redback Spiders rarely leave their webs, humans are not likely to be bitten unless a body part such as a hand is put directly into the web, and because of their small jaws many bites are ineffective. The venom acts directly on the nerves, resulting in release and subsequent depletion of neurotransmitters.
Common early symptoms are pain (which can become severe), sweating (always including local sweating at bite site), muscular weakness, nausea and vomiting. Antivenom is available. No deaths have occurred since its introduction.
Apply an ice pack to the bitten area to relieve pain. Do not apply a pressure bandage (venom movement is slow and pressure worsens pain). Collect the spider for positive identification. Seek medical attention.
Classification
- Species:
- hasselti
- Genus:
- Latrodectus
- Family:
- Theridiidae
- Order:
- Araneae
- Class:
- Arachnida
- Phylum:
- Arthropoda
- Kingdom:
- Animalia
References
- Simon-Brunet, S. 1994. The Silken Web: a natural history of Australian Spiders. Reed Books.
- Preston-Mafham, R. 1991. The Book of Spiders and Scorpions. Quarto Publishing.
- Pyers, G. 1999. Australian Animals: Spiders. Heinemann Library.
- Forster, L. 1995. The behavioural ecology of Latrodectus hasselti (Thorell), the Australian Redback Spider (Araneae: Theridiidae): a review. Records of the Western Australian Museum Supplement No. 52: 13-24.
- York Main, B. 1976. Spiders. The Australian Naturalist Library, Collins, Sydney.
- Garb, J. E., A. Gonzalez, & R. G. Gillespie (2004). The black widow spider genus Latrodectus (Araneae: Theridiidae): phylogeny, biogeography, and invasion history. Molecular Phylogenetics and Evolution. 31, 1127-1142.
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11 comments
Martyn Robinson
11.02 AM, 04 February 2010
Hello Gazza & Josh,
Gazza- male Redbacks are considered harmless as they are so tiny their fangs would have difficulty piercing skin anyway. However, as you found a male the chances that there are females nearby is pretty high. You might want to remove them from inside your house but what you decide to do with them then is up to you. If they don't bother you or your neighbors then you can just ignore them. They are as good at insect control as any other similar spider.
Josh - I don't think you can get antivenom for home use as it should be administered by someone in the medical profession and stored carefully before use. It should be realised that for MOST people the treatment for Redback bites is simply an ice-pack to reduce the swelling and pain. However as Ondine says treat all bites as potentially serious particularly if children or people with allergies to insect stings are concerned, until told otherwise by a doctor.
The other important thing to note is that bites are rare compared to most other accidents and you have to be very unlucky to be bitten. Redbacks are very common in many areas and people have lived alongside them with mostly few problems for all of Australia's human history. Death by lightning strike is 19 times more likely than death from spider bite and no-one has died from spider bite in Australia since 1980. Certainly take care, warn children what not to do, and remove any Redbacks from areas where they might cause problems (e.g. inside the house) but dangers from spiders are very exaggerated.
Sincerely
Martyn Robinson
Josh
2.02 PM, 03 February 2010
Hello we have just recently found and killed 26 redbacks in a week last night 16 is there a way that you would be able to get hold of anti venom and supply it in your first aid kit because 26 in the one spot but spreaded out a 1 Mtr is a worry and out in the open were you walk please email me at joshua-parker@hotmail.com under spider for the subject
Gazza
11.01 PM, 30 January 2010
Hello, I found a redback I do believe Male as it was quite slender in a web underneath my oven. I took the redback outside carefully watching it and brushed it into the garden. Should I have killed it? Is it true the male is not deadly? Are there likely to be others around? So many questions. Im jumpy right now and checking for webs everywhere.
Ondine Evans
10.01 AM, 27 January 2010
Hi countryaustraliaa - A Redback Spider bite is a serious prospect for anyone. However, it is a fact that people with compromised immunity, children and the elderly may be even more susceptible to toxic spider and other bites. In ANY case, treat all suspected venomous bites as potentially dangerous and seek medical attention immediately. Our page on Spider bites and venoms has more information about how venoms work and also first aid for bites. Note that Pressure immoblisation is NOT recommended for Redback bites as it actually increases pain. However, if you have not caught, or definitely identified, the spider (or other animal) responsible, you must treat any bite as possibly dangerous until proven otherwise.
countryaustraliaa
6.01 PM, 24 January 2010
Are redbacked spider bites dangerous to pregnet women?
Ondine Evans
10.01 AM, 14 January 2010
Tasdevil, you have raised an interesting point of discussion. I have contacted our Arachnology section, which has provided me with some information and a reference to a research paper, both of which I have added to the main page above. See Evolutionary Relationships (and the reference is the last one listed). An interesting line of thought!
tasdevil
10.01 PM, 09 January 2010
Hi. my uncle told me there was debate in the scientific community whether the redback was indeed native to australia as they were only "discovered" recently (maybe 100 years ago - what about the other 120 years of our post first-fleet history??). Also he said there was no aboriginal word nor mythology for the redback (yet there is for the funnel-web). So I went to the library got out a book on australian spiders it said the same thing. The author suspected it was really the black widow that came over and the different markings are a result of evolution (BTW I have seen black widows when i lived in california they look almost identical in size/shape/markings and their webs). Has there been any DNA testing yet to ascertain native status? (I need to know whether to kill them as in introduced pest or to leave them be as a native species). Thank you.
Martyn Robinson
11.01 AM, 05 January 2010
Hello Nicky,
Ondine's suggestion is a good one but if you're nervous of spiders you might want to get someone else to do this. Alternately you could spray the inside of your letterbox with either Citronella or Eucalyptus oils. This will drive the spider out and the residual odour will prevent others from taking up residence.
'magpies' your roof spiders may well be Red-backs but check that they DO actually have red backs as there's some very similar spiders which lack this marking. They aren't colonial but an area where there is a lot of food will often attract quite a few and allow them to survive in close proximity to one another. As to the roof being a suitable site - it's certainly possible but they are usually closer to ground level.
S
M
magpies
9.01 AM, 05 January 2010
hi, i have been told that i have a group of redback spiders in my roof? is it common for them to be in a group? and in a roof? thanks earl
Ondine Evans
11.01 AM, 04 January 2010
Hi Nicky. Redback Spiders are not particularly jumpy, so you could probably stick a feather duster or small brush in there, swirl it around to get the web and spider, then extract it all and dispose of it away from the letterbox. Wear thick gloves if you are a bit concerned about it getting on you!
nicky
6.01 PM, 03 January 2010
There's a red back in my letter box. Any ideas how to get it out with out spraying insecticide?
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