Redback Spider What is a Redback Spider?
Redback spiders are found throughout Australia. The female is highly venomous, and is easily identified by her jet black pea-shaped body with a distinct red or orange stripe on top — a clear warning to predators (and foolish humans) to keep away.
Description of the Redback Spider What Does a Redback Spider Look Like?
Spiders are not Insects
While spiders may look like insects, they are actually arachnids and belong to the same family as scorpions and ticks. An arachnid has two body parts, eight legs, no antennae or wings and cannot chew its food; its sucks juices instead. There are over 40,000 different species of spiders in the world.
Red back spider (Latrodectus hasselti) females have a body length of about 10mm. Besides the distinct markings on top of her body she also has an hourglass shaped marking on the underside of her body.
While the female has a pea-shaped body, the male has a long, light brown body with similar but much paler markings and at 4 mm in length he is about 60% smaller than the female and may weight as little as 1% the weight of a female. Male redback spiders are inconspicuous compared to the female, do not build webs, are not venomous to humans and rarely seen except during mating season. Juvenile female redback spiders have a number of camouflage-like white markings on their abdomen. The redback spider is related to the black widow spider found in the United States.
The redback spider's body consists of two parts. The front part which is referred to as the cephalothorax contains eight tiny eyes, brain, mouth consisting of a tube similar to a feeding straw, its chelicerae which are pincers with inbuilt fangs, pedipalps which are a set of arms for holding prey, venom glands, a sucking stomach and all of its eight long legs. (See diagram).
The second part of its body is its abdomen, located immediately behind the cephalothorax and joined to it by a thin flexible waist called a pedicel. This acts like a joint, allowing the spider to move its abdomen without moving its cephalothorax.
The abdomen contains its lungs, heart, intestine, reproductive organs, silk glands and spinnerets from which it produces its silk.
Redback Spider's Web Redback Spider's Web Construction
The redback spider’s web appears like a rather messy unstructured tangle of randomly placed threads affixed to supporting surroundings. Although haphazard in appearance these silk threads with globules of sticky glue are in fact deliberately positioned to ensnare prey. The web consists of numerous sticky catching threads which trap any creature that comes in contact with them and act as tripwires to alert the spider of activity in its web. As its prey tries to free itself from the web it is more and more entangled by the strands of silk and held captive for the coup de grace — the deadly bite of death, to be inflected by the spider.
The web narrows at the back into a denser funnel-like area where the spider rests and stores its egg sacs. During cooler weather, when the spider is less active, it also shelters in this area and is rarely seen. Being mainly nocturnal, the female coming out at night to spin and repair her web. Once her work is done she waits patiently, sometimes for months, until food arrives.
Redback Spider Diet How the Redback Spider Catches and Eats Prey
What Do Redback Spiders Eat?
Redback spiders are carnivorous predators. They prey on insects, small lizards or any other animals that may get ensnared in their webs. They are not intimidated by the size of their prey that could be many time larger than themselves. There is even a video of a redback spider attacking a venamous red bellied black snake ensnared in its web. Female redback also steal food packets stored away by other spiders. It can survive for as long as 3 months without a meal.
Dinner is Served
Having built and maintained its web the redback spider waits patiently for some hapless prey to run into its trap. In the case of smaller prey, like an ant, the thread to which the ant has got stuck will snap when it struggles and flip the little insect further up into the web, truly trapping it. In the case of larger prey the more it struggles the more it will get trapped by the many strands of the spider's sticky web. Shockwaves will immediately reverberate across the web altering the spider to some promising activity on its web (It knows to ignore inconsequential incidents such as the wind, or a leaf hitting its web etc. and is well attuned to animate vibrations when they occur).
Alerted by these shockwaves from a struggling victim, the redback spider will approach cautiously to investigate. It reaches out and gently touches and smells its prey with the tips of its feet to determine if it is edible or not. If edible the spider sets to work securing its meal. If the prey is not securely snared, the spider will set to work wrapping the hapless victim in more of its incredibly strong silk threads until the prey is held firmly and cannot retaliate. The it will then administer the fatal blow — the coup de grace — by biting repeatedly with its pincers and injecting neurotoxic venom into its prey paralysing and killing it. Once its victim is dead, the redback spider will haul it, if necessary, higher into its web to a suitable feeding station.
Only Soup Please and Through a Straw
The redback spider, like all arachnids, has no mouth parts for chewing its meals. It can only suck its meal in liquid form. So it injects very powerful digestive enzymes into its prey. These enzymes breakdown and dissolve the victim's tissue which the spider then sucks up with its straw-like mouth.
Redback Spider Reproduction The Fatal Mating Ritual of the Redback Spider
Attracting a Partner
A female redback spider secretes sex pheromones onto her web advertising to potential suitors that she is available to mate. A male may journey towards and signal from a safe distance to her to determine if she is receptive to his advances, as any false move on his part could result in her mistaking him for a snack. If she responses non-aggressively he will approach her.
The male redback spider does not have a penis or any other structure to directly transfer sperm from his gonads and deposit it in the female spider's sexual organs. So he has devised an ingenious solution. The male spider collects his sperm from his gonads and enclosed it in a special sac he constructs with silk he releases from his pedipalps (the pair of arm-like appendages on its cephalothorax) and affixes these sperm sacs to each of his pedipalps.
Head Stands a & Sexual Cannibalism
During mating the male redback spider, attempts to deposit his sperm sacs inside the female’s sperm receptacles (spermathecae), located on the underside of her body at the front of her abdomen. The only way he can do this is to stand on his head and try to reach under her with his pedipalps. Unfortunately for him while he is attempting to deposit his sperm she squirts her powerful digestive enzymes onto his exposed underbelly dissolving him alive. If he is lucky he may deposit one or both his sperm sacs inside her before he dies as a result of his dissolving body. The female will then go on to feed on the male.
Once the female has mated, she can hold the male's sperm in reserve and use it over a period of up to two years using it to fertilise several batches of eggs. Given this characteristic she may mate only once in her lifetime.
Redback Spider Life-cycle Paragliding Away
Once she has mated, the female redback spider constructs 2–10 silken egg sacs, usually about 1cm in diameter and white in colour, and deposits up to 250 eggs into each. These egg sacs are firmly affixed to the back of her web. Depending on the weather, young spiderlings hatch in two to four weeks.
Young spiderlings have an interesting way of leaving home. When it is time to leave they stick their abdomens high in the air, to catch the wind, and release a droplet of liquid silk which gets drawn out by the wind and until it forms a long gossamer thread that acts like a paraglider and lifts the little spider and carries it with the air currents on a perilous journey to a new location. Eventually the thread will entangle or adhere to an object and the young spider will attempt to establish a web of own there.
Redback spider males reach maturity in about 3 months and females in about 4 months. However, very few redback spiderlings survive to reach adulthood as they may be eaten by their siblings, fall prey to predators or become the host to wasp parasites that feed on them.
Male redback spiders live for 6–7 months and the females may live for as long as 2–3 years.
Redback Spider Habitat Where Do Redback Spiders Live?
The Redback spiders are found throughout most of Australia where it is warm enough for breeding, there is an adequate food supply and shelter. Female redback spiders build their webs in dry, dark, protected areas with sufficient structures for it to hang its web such as crevices, shrubs, logs and tree hollows close to ground level. Male spiders do not build nests but are free roaming. Redback spiders are sedentary, that is, they remain in the same location for their entire lives.
Cohabitation with Humans
Redback spiders seem to like living close to human habitation and are most frequently found in urban areas. The reason for this may be in increased concentration of insects and other prey in these environments. They may be found, in gardens, verandas, in woodpiles, outdoor furniture or inside a building in any location. A standing Australian joke is being bitten by a redback while seated on the toilet. And, believe it or not, such instances have actually happened.
Is It Really Native?
There is some speculation that redback spiders may has been introduced to Australia as a consequence of European settlement. This is because they were first discovered close to seaports and only reported nearly 75 years after the first Europeans arrived. This suggests they may have come aboard incoming vessels from Asian where the animal is also said to exist. Others dispute this theory and claim that the redback spider is
Predators, Parasites and Diseases Threats to Redback Spiders
Daddy-long-legs Spiders and white-tailed spiders prey on redback spiders. Ichneumonid wasps sometimes puncture a small hole in a redback spider’s egg sac and deposit its eggs there. The young wasp larvae then feed on the little redback spiderlings. Redback spiders are not endangered.
How to Get Bitten by a Redback Spider
A redback spider is not going to jump out and bite you. Unfortunately these spiders like the structures humans build and build their webs in our structures. Most bites occur as a result of humans intentionally or unintentionally invading the "space" of the spider. It is the spider's natural defence is to bite. Most bites occur between December and April, in the afternoon or evening.
What to Do if Bitten
Redback venom acts very slowly on humans giving you plenty of time to seek medical treatment. Usually a bite isn't immediately apparent. Pain sets in 5–60 minutes after the bite and within an hour the entire limb will be painful and sweating will commence. Do not apply a constrictive bandage, the pressure will merely increase the pain. The only recommended action is to administer ice packs to the bite site to help reduce the pain and seek medical attention promptly.
At least 2000 redback spider bites are recorded in Australia each year. Of these about 250 people have required antivenom treatment. In most instance insufficient venom was injected into the victim to be fatal. While there have been no recorded death since the antivenom was first introduced in 1956. One unsubstantiated death of a 22 year old male occurred recently. Prior to the introduction of antivenom 14 deaths were recorded.
Thick clothing, gloves and not poking your hands into places without first checking are some of the simplest precautions against spider bites.
What Venom Does the Redback Spider Produce?
Wondered why we keep using the term 'venomous' rather than 'poisonous'? Here is the reason. A venomous animal injects or otherwise delivers its toxin into another animal. While a poisonous animal's entire body or parts of it may be contain a toxic substance that is harmful if touched or eaten. Because the spider injects its toxins it is venomous.
The venom of a redback spider is a complex cocktail of toxins and enzymes. These include neurotics which effects the nervous system, myotoxins which effects muscles, haemorrhagins damage the blood vessels and cause bleeding, haemotoxins: destroys the blood, nephrotoxins lead to kidneys failure, cardiotoxins effects the heart and necrotoxins which kills body cells and causes necrosis (dead body tissue). The most potent of these is the neurotoxin called alpha-latrotoxin, which effects vertebrates including humans, causing the over stimulation of neural pathways of the body with a wide range of effects. These include a stinging sensation when first bitten which can become excruciatingly painful, draining of the lymph nodes in the groin, pain throughout the abdomen, chest, neck and head, profuse sweating, mild to severe hypertension and nausea.
How Toxic is Redback Spider Venom?
The venom produced by the redback spider is more potent than that produced by a king cobra. It would take 136mg of cobra venom to kill an adult male weighing 78kgs. It would take just 46mg of redback spider venom to do the same job. That is roughly 1/3 less.
How is venom Injected?
Only the female redback spider produces venom that is noticeably dangerous to humans. Venom is produced in two glands located in its cephalothorax and expelled through a pair of ducts through its pincers (chelicerae) and finally through its piercing hollow fangs. Redback spiders fangs, at just 0.7mm, are very short, typically if bitten through clothing its will not reach the skin.
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