Red-back Spider Reproduction
By Kira Maher
The Red-backed spider lives in a terrestrial environment; often found in close proximity to human residence. They are found in most parts of Australia, in sheltered, dry places; for example, under rocks or logs, or in sheds. They create and live in sticky, tangled, funnel shaped webs in these areas. Problems that come with this habitat are the threat of humans. The bite of a Red Back spider is venomous, and because of this, humans often clear away their habitats and kill them.
Map of Australia showing the distribution of Redback spiders.
After having mated, female Red back spiders store the sperm in the spermathecae; (sperm storage organs) and can use them to fertilise and lay several batches of eggs at any time. Females lay between 4 and 10 egg sacs, each containing around 250 eggs. Eggs hatch after around 8 days, and spiderlings disperse on the wind. Female spiders will mature within 4 months of age and can live for up to 2 or 3 years, while males mature in 90 days, and only live for 6 or 7 months.
Anatomy of a Redback spider
Redback spiders reproduce sexually (by cross-fertilisation), and fertilise internally, although indirectly. This means that the male does not deposit the sperm directly into the female's ovaries. The sperm is stored, and used by the female when required. Copulation is unique in Redback spiders, as they undergo a process called sexual cannibalism. Sexual cannibalism, as the name suggests, involves the female consuming the male during the process of copulation. The male spider approaches the female; this is risky, as the female could potentially mistake it for prey; and inserts one of its pedipalps (a limb-like extension used to insert sperm) into the female's spermathecae. While doing this, it will twist it's body 180 degrees and place it's abdomen in front of the female's fangs. The female begins to consume the male spider's abdomen. Most male spiders will survive this, and repeat the same action with the other pedipalp being inserted into the second spermathecae. The female will continue to ingest the male, 65% of males ending up being consumed entirely. The exact number of gametes released are unknown, but it can be assumed that it is quite a large number, based on the number of offspring produced by the female. Advantages of releasing many gametes are that it ensures that many eggs will be fertilised and many offspring will be produced.
The embryo develops externally in the egg sac laid by the female spider. Redback spiders are oviparous, meaning that they produce eggs which hatch outside the body. The Redback spider most likely uses this method as it lives in protected, sheltered, dry areas. The eggs will grow in a sheltered environment, making it safer to have the spiders develop outside the body. This means that the egg sac is less likely to be destroyed or eaten by other creatures; however, humans do pose a threat to this method. The gestation period for Redback spiders (or from the egg to the spiders emerging) is between 17 and 43 days, 28.7 days being the average. This short gestation period means that offspring are able to be born and disperse quickly, which is necessary because of the fairly short lifespan. Disadvantages of this are that the species are less developed than K-selected species.
The Redback spider is R-selected, meaning that it produces large numbers of offspring, matures quickly and has a short life, and has a short gestation period. Shortly after birth, spiderlings disperse from the maternal web on the wind, meaning that mothers give their young very little or no parental care. The exact mortality rate of Redback spiderlings is difficult to gauge as the spread out so widely, however, they are known to demonstrate cannibalistic tendencies and eat their siblings, so only the strongest will survive. Advantages of this strategy are that they spread out over great distances and in such large numbers, that many are sure to survive and set up webs to ensure that the species is kept alive. Disadvantages of this strategy are that they die quickly, meaning that there may not be enough time to find a mate and reproduce. 80% of males will die without having found a mate.
- The Redback spider is one of two known species in the world where the male actively assists the female consume him in sexual cannibalism.
Female spiders can use sperm deposited by the male for up to two years after mating.
- Redback spider. (2013). Retrieved September
14, 2013, from Wikipedia: http://en.wikipedia.org/wiki/Redback_spider
- Bindman, A. (2013). Latrodectus Hasselti. Retrieved September 16, 2013, from Animal Diversity Web: http://animaldiversity.ummz.umich.edu/accounts/Latrodectus_hasselti/
- Redback Spider. (2011). Retrieved September 15, 2013, from CSIRO:
Redback Spider, Latrodectus hasselti . (2013, September 11). Retrieved September 15, 2013, from Australian Museum: http://australianmuseum.net.au/Redback-Spider