Battles to the death are taking place across Australia as sisters fight it out for the family home.
Dr Linda Rayor, a visiting fellow at the Australian National University in Canberra, uncovered the gruesome family feuds while studying the tree-dwelling species of huntsman spider Delena cancerides.
Rayor, from Cornell University's Department of Entomology, says her study of D. cancerides has shown it is the only one of the 1039 known huntsman species that lives a social life with family members.
Among the world's 40,000 known spider species only 1% are social with this species one of only two that does not spin a web.
Redback spiders sniff air then mature
Australian redback spiders sniff out how much competition they have for females as they're growing up, and tailor their adult size accordingly, say Canadian researchers.
Michael Kasumovic and Dr Maydianne Andrade of the University of Toronto report their findings in the latest issue of the journal Current Biology.
"Males are really tracking the selection pressures that they're facing in an environment. They're aware of male density and the amount of competition they're going to be facing," says Kasumovic.
Like most spiders, male redback spiders are much smaller than the females but they vary in size.
Kasumovic and Andrade have found that an individual spider's development is determined by a trade-off between traits that benefit a spider's sexual success versus their longer term survival.
"A trait that's good for sex is often not good for surviving and a trait that's very good for surviving may not be good for sex," says Australian spider expert, Dr Marie Herberstein, of Macquarie University in Sydney.
The classic example is the male peacock's tail, she says, which is good for attracting females but weighs him down and affects his chances of survival when being pursued by a predator.
She says Kasumovic and Andrade have found that when it comes to the redbacks, maturing early is good for their sexual success but maturing later is better for survival.
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