Full classification, kingdom through to species:
Kingdom: Animalia, Phylum: Arthropoda, Class: Arachnida, Order: Araneae, Family: Theridiidae, Genus: Latrodectus, Species: L. hasseltii
The redback spider is one of the most dangerous spiders in Australia and are one of the country’s icons. The females are easy to identify because of the distinctive bright red stripe found on their abdomens. The rest of their bodies are black (or sometimes dark brown) and their bodies measure about ten millimetres long usually (about the size of a large pea). The purpose of their eye catching colouring is to warn potential predators away. Many creatures associate strong colours with poison and bad taste and are therefore more likely to stay away from them.
The female redback is the third most poisonous spider in the world and it is possible for their bites to be fatal to humans if left untreated. Each year around two thousand people report bites and roughly 250 are given antivenom. Since an antivenom was created in 1965 there have been no human deaths. The males are much more plain looking and far less dangerous as their fangs can’t usually penetrate human skin. They are not seen often and are tiny in comparison to females with only three to four millimetre long bodies (see picture to the left). They are predominantly brown in colour, sometimes with small white, yellow or red markings on the body. Also, they don’t live as long as the females.
As arachnids, redbacks have eight legs that are thin and each usually longer than their bodies to allow them to move quickly and reach further. The legs have tiny hairs on them that pick up vibrations and smells from the air and the tips of their limbs are designed to grip their webs and allow them to stick to other surfaces. Their bodies are made up of a large round abdomen containing the lungs, heart and reproductive organs, and the head section (cephalothorax) which contains the brain, stomach and poison glands. At the front of the head are small fangs used to inject venom into their prey, their eight tiny eyes and their pedipalps. At the back of the abdomen is their spinnerets used to make their webs.
Redbacks are native to Australia and can be found almost throughout the country. They are often found in cities and in urban areas as well as in wild areas like forests and deserts. They prefer dry environments to moist areas but can survive in many conditions. They have high temperature tolerances and can therefore live through extreme heat or cold. Webs can usually be found in dry, dark, sheltered areas like under or between rocks, in shrubs, old tires, stacks of wood, tree hollows, logs, sheds, empty tins or boxes, large discarded rubbish piles, unused outdoor furniture, around building foundations, under houses, in rooves, letterboxes or famously, underneath toilet seats. Their webs are messy and tangled compared to other spiders and have no apparent pattern. Only females produce webs.
Redbacks are arachnids, meaning that they produce eggs, which their babies then hatch out from. The female produces up to ten round egg sacs which are white in colour and about 1cm long. Within each sac is roughly 250 eggs. The sacs are stuck to the webs and the spiders hatch in two to four weeks. However, if they are located in a very cool environment they can take much longer to hatch. The baby spiders (called spiderlings) eat unhatched eggs and other spiderlings once they are born and then move to another area by using air currents to blow them.
Females become mature after being alive for about four months whereas males take about 90 days usually. Before they die, females live for between two and three years in total and males have significantly shorter lifespans of around six or seven months. They usually mate during the summer season more than in winter and during this time males can often be seen on the edges of a female’s web. They are able to detect the pheromones which the female secretes and this attracts them to sexually mature females.
The male approaches the female to see if she is ready to mate and if she is not, he will often be killed by the female. Even if the female is ready to breed, the males don’t usually survive the mating process and are often eaten by the females. Females are able to store the male’s sperm after they have mated for a few years afterwards. During this time she can use it to produce many batches of eggs.
Redbacks are carnivores/insectivores. This means that they eat insects and other animals but don’t eat plants. Any animal that becomes tangled in their web is possible prey for them and the majority of their diet is made up of insects. One of the main reasons they are commonly found in areas near humans is that their prey are often attracted to the food scraps and light in urban areas.
Although they primarily eat insects, they are also able to eat much larger creatures such as small lizards, other spiders like the trapdoor spider, king crickets, small lizards (like skinks), small frogs and occasionally even mice. Large female redbacks have also been known to steal prey from the webs of fellow spiders and engage in fights if the other spider tries to defend its food. Whichever spider is successful usually eats the other.
The male redback can survive for very long periods of time without eating and may fast while in search of a mate for weeks. When a female has accepted a male’s offer to mate she may share some of her food with him.
Once a creature is tangled in the female redback’s sticky web, they are sprayed by the redback with a strong glue like material to further trap them and reduce their ability to move. After this is complete the redback starts biting the creature many times all over the body, targeting areas such as the head and joints before wrapping it in its silk (the same material used to construct the webs). Finally, the spiders imject their venom to turn the creature’s insides into a liquid and then suck out this liquid.
- The redback spider is closely related to the famous American Black Widow spider.
- Redback spider bites can cause sweating, nausea, headache, abdominal pain, vomiting, fever, parenthesis, hypertension and rashes.
- It is possible for female redback spiders to not possess a red stripe.
- Other spiders such as the daddy long legs and the white tail spider can kill redback spiders.
- There is a song called the “The Redback on the Toilet Seat” which was written by Slim Newton and released in 1972 and it reached number three on a national singles chart.
Redback egg sacks are often destroyed by wasp parasitism.