Redback Spider Fact File
The redback is most recognizable due to the large red stripe running down the back of the females abdomen. Females and males have markedly different appearances. Both have eight legs with the front pair being longer than the other three pairs.
Females are the most commonly seen of these spiders. They have a large body of up to 10mm (0.4in) in length. This is coloured black or dark brown across most of their body with a large red or orange stripe running across their abdomen. They also have a red hourglass shaped marking on their underside.
Males are much smaller than females at 4mm (0.16in) and typically live on her web. They are light brown or black with white stripes on their body and small red markings. On their underside the hourglass marking is pale.
They also scavenge food out of the webs of other spiders.
Males live on the edge of a females web for most of their life and will typically take food scraps she leaves behind.
Once food is stuck in the web they will turn their back to it and cover it with lines of sticky silk. Once it is fully bound in silk they will bite it and inject their venom before they take the prey item to the top of their web to be eaten.
Male 4mm (0.16in)
Female 10mm (0.4in)
Male 7 months
Female 3 years
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The native home of the redback spider is Australia. Here they can be found across most of the country.
Introduced populations have spread to New Zealand on imports of grapes. They have also spread to Asia where a confirmed population exists in Japan with other populations beginning to establish in parts of South-East Asia.
Naturally they occur in savanna, temperate, tropical and desert areas. While they are not typically found at high elevations they can occur in cold areas.
The expansion of human habitations has assisted the redback spider which survives successfully in their homes.
Breeding may take place year round though peaks during summer.
Females mate with multiple males though males often typically only mate once in their life as a result of the females tendency to eat males at the conclusion of mating.
During the mating season a number of males may congregate on the web of a single female. These males may fight one another for mating rights and often this is fatal for one of the contenders.
Males approach the female and attempt to insert a pedipalp (a small appendage that looks like a miniature leg on either side of the mouth) in to her sperm storage organ. In an attempt to distract the female while he mates with her he will stand on his head and allow her to begin to eat his abdomen while he mates with her. This is why males often do not survive mating.
Following a successful mating the male may break off part of his body to plug the females sperm storage organ and prevent other males from mating with her.
Once a male has mated with the female she may store that sperm and use it to produce eggs for up to 2 years. In this time she can produce as many as 10 egg sacs. These are coloured white when laid but weather to brown as time goes on.
Each egg sac is deposited on the web and these can contain as many as 250 eggs. The eggs incubate for two to four weeks. After hatching they are cannibalistic and eat any unhatched eggs or their siblings which are yet to leave the nest.
Once they are finished eating they will throw a silk line which catches on the wind and carries them to a site where they can create a web. This process is called ballooning.
Males take three months to mature with females maturing slightly later at 4 months old.
Redback spiders live on a web. This is made up of two parts. The top part is where the spider lives and creates their egg sac. It also creates the structural support for the lower part of the web which traps their prey. This area consists of a range of vertical trip lines coated with liquid silk which glues prey to the web.
Predators and Threats
They are eaten by the daddy long legs and white tailed spiders.
Humans often kill the redback spider when they find them around their homes due to the danger presented by them.
Their main defense is their highly potent venom which is a latrotoxin and acts on the nervous system of their prey.
Up to 250 people require treatment each year for redback spider bites in Australia. This is in addition to many bites which do not require treatment due to the severity of the bite.
While the venom of a redback can cause death none have been recorded since the invention of antivenom in 1956. The effect of their venom on humans is typically slow but if you are bitten always seek treatment from a medical professional.
Fir0002/ CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/)
By Wocky – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=9754110
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