Female sex cannibals not angry, just picky, spider study finds

The female raft spider – often accused of indiscriminate aggression for cannibalising her potential suitors – is actually testing the worth of her mates, a new study suggests.

The research challenges a popular idea that sexual cannibalism occurs because the female is unable to alter or 'tone down' her aggressive mindset after foraging and hunting for prey.

But researchers, including University of Melbourne scientist Mark Elgar, suggest the raft spider, Dolomedes fimbriatus, should be given a bit more credit.

"Females are sexually canniblistic because they are testing the males, rather than just being inherently aggressive," Dr Elgar said.

In the first trial, 11 of 16 females that copulated then attacked the males during or immediately after copulation. But only four attacks were fatal.

In the second, six of eight females that copulated attacked the males, with two fatal attacks.

"We conducted extensive experiments and found no correlation between female foraging aggression and that displayed towards males," Dr Elgar said.

"It actually appears there are many other potential factors involved, including the size of the males in comparison to the female, the female's age and whether or not she is a virgin."

Although more than half of the females tested were aggressive in sequential mating trials, females were not consistently aggressive: females that were aggressive in one trial were not nessarily aggressive in the next.

"Females were marginally more likely to attack smaller males, and that's perhaps because they are easier to capture," Dr Elgar said.

The raft spider, found around Europe near bogs and wet grasslands, is one of several arachnid species and other insects that are known to cannibalise their male counterparts.