Reproduction
The redback spider is one of only two animals to date where the male has been found to actively assist the female in sexual cannibalism. In the process of mating, the much smaller male somersaults to place his abdomen over the female's mouthparts. In about two of three cases, the female fully consumes the male while mating continues. Males which are not eaten die of their injuries soon after mating.
Sacrifice during mating is thought to confer two advantages to the males. The first is the eating process allows for a longer period of copulation and thus fertilisation of more eggs. The second is females which have eaten a male are more likely to reject subsequent males. Although this prohibits the possibility of future mating for the males, this is not a serious disadvantage, because the spiders are sufficiently sparse that only 20% of males ever find a potential mate during their lifetimes.
Some redback males have been observed using an alternative tactic that also ensures more of their genetic material is passed on. Juvenile female redbacks nearing their final moulting and adulthood have fully formed reproductive organs, but lack openings in the exoskeleton that allow access to the organs. Males will bite through the exoskeleton and deliver sperm to the organs without performing the somersault seen in males mating with adult females. The females then moult within a few days and deliver a normal clutch of eggs.
Once the female has mated, she can store sperm and use it over a period of up to two years to lay several batches of eggs. A female spider may lay eggs every 25 to 30 days. A single female normally lays between 40 and 300 eggs in each sac, but can lay up to 5000 eggs. The eggs hatch 13 to 15 days after being laid. Young redback spiders leave the maternal web by being carried on the wind. The spider extends its abdomen high in the air and produces a droplet of silk. The liquid silk is drawn out into a long gossamer thread that, when long enough, carries the spider away. Eventually, the silken thread will adhere to an object where the young spider will establish its own web.
Read more about this topic: Redback Spider
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