Redback Spider

800px-CSIRO_ScienceImage_3797_A_Redback_Spider

Profile

Redback spiders are small venomous spiders living in Australia and New Zealand. If you don’t pay VERY close attention, these spiders can easily be confused for black widow spiders. In fact, these two spider species are in the same genus! The first word in their scientific names are the same! Females look almost exactly the same from the underside, as both have a red hourglass shape.  One difference between the female redback spiders and female black widow spiders is the namesake of the former: her red back. While the back of a female black widow spider is completely black, the redback spider ladies have a red stripe on the rear half of their back. Males, which look much different from the females, also look somewhat like black widow males. They have brown and black legs, a black head, and a white, brown, and tan body with interesting markings. As you can see from the picture below, the males are much different than the females.

male_redback

Size

Not only do males and females look very different, they also have a much different size. Males are much smaller than females, yet another similarity to black widow spiders. You know, with all this similarities you can kind of tell why these two species were put in the same genus. Females can have a body length of up to 0.4 inches (1 cm), while the males are only about 0.15 inches (4 mm) long.

I could not find a leg-span measurement for these spiders, but we can guess. The female in the top picture looks like the body is a little less than half her leg-span. This would make her be about one inch (2.5 cm) from leg tip to leg tip. The male has much longer legs compared to his body, a measurement that looks about one quarter of his leg-span. This would put his measurement at approximately 0.6 inches (1.5 cm). Again, these are just estimates to give you a rough idea, not actual measurements.

Diet

Redback spiders eat mainly insects. I mean, they’re spiders. What did you expect? Their meals can include flies, mosquitoes, moths, and cockroaches. They eat not only insects but also spiders, such as the trapdoor spider or the funnel-web spider. Although invertebrates make up almost all of this spider’s diet, they also consume a few vertebrates. One of the most common of these is small lizards, which sometimes get caught in the sticky webs. These spiders do not need to eat frequently, as adults have been known to survive almost one year of not eating! Although they become extremely sluggish as time goes on, they recover almost immediately after eating.

Venom

Redback spiders are venomous, but only the females have this venom. The venom attacks the nervous system, but is usually not deadly. About eighty percent of bites have no effect or little effect. This is probably because these spiders can control the amount of venom they inject. They sometimes bite and don’t inject any venom at all. Most of the rest of the bites result in minor pain around the bite. More serious bites cause increased heart rate, vomiting, headaches, and swollen lymph nodes. Because an anti-venom is present, fatalities are few, and there have been none since 1956 when the anti-venom was created. About 250 victims receive this anti-venom yearly. These spiders are not very aggressive, and will usually only bite if part of someone’s body is put into its web.

Habitat and range

Redback spiders are native to all areas of Australia. They have also been introduced to both the North and South islands of New Zealand via grapes being imported from Australia. They are sometimes seen in other countries also, such as Japan, India, and many other countries of Southeast Asia. Redback spiders are normally found in urban areas and particularly like living in houses. This protects then from many predators as well as bad weather. When there are no suitable buildings around, these spiders will make their webs in other sheltered areas such as under logs and among rocks.

Status and threats

The redback spider has not been classified by the IUCN Redlist. Most spiders are not classified, as they are relatively common, and people usually don’t care if spiders are endangered. If this spider were classified, I think it would be Least Concern. This is because they have a large range and have even been introduced to other places besides their native range. The main predators of this spider are other spiders, such as the daddy-long-legs. Some small wasps will infiltrate redback spider egg sacs and consume the eggs. Of course humans also try to kill these spiders, especially since they are venomous.

Reproduction, eggs, and young

Although redback spiders can mate year round, they prefer to do this in the summer when temperatures are higher. When males mate with the females, they must put themselves in a position with their abdomen right under the female’s fangs, While mating, she starts trying to eat him. Most of the males get free, though. The males then mate a second time with the same female, and about 65% of the time, the female is successful in consuming the male after this. Although mating is dangerous, the males will actually compete for the right to mate with a female. Because the female eats her mates afterwards, she is able to mate with many different males. Females can wait up to two years after mating to lay her eggs. These eggs are laid in egg sacs with up to 250 eggs in each, and she can make up to 10 egg sacs each time she lays eggs.

The egg sacs, which are suspended in the web, are white right after they are made, but they soon turn brown. Depending on the temperature, the eggs can take between 17 and 43 days to hatch with higher temperatures resulting in a shorter length of time. The average time it takes the eggs to develop and hatch is about four weeks. Females are ready to mate less than four months after they hatch, and males less than three months. The picture below shows a juvenile female, which looks much different than the adult females do.

Female redback spiders can live up to three years in the wild. Because mating is so dangerous for the males, they usually only live for at most seven months.

Juvenile female redback

Don’t forget to scroll down and comment your guess about what the next animal is!

569px-Cetorhinus_maximus_by_greg_skomal

Sources:

Photo credits:

  • Redback Spider – David McClenaghan
  • Male redback spider – Jean Hort
  • Juvenile Female redback spider – Jean Hort
  • Mystery animal – Public Domain
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