Spiders behaving badly

How do you decide whether or not to pick a fight with someone? Good advice on this matter is to be found in a couple of recent papers in the journal Animal Behaviour. In "Experience influences male-male contests in the spider Argyrodes antipodiana (Theridiidae: Araneae)", Mary EA Whitehouse points out that "it is to an animal's advantage to assess the abilities of its opponent and compete more strongly against weaker competitors and avoid contests with stronger competitors".

To see whether spiders had the common sense to follow that advice, contests were set up between male spiders competing for the same female. "Three types of male-male interactions were observed: type 1, where one male immediately mated with the female without first interacting with the other male; type 2, where males held a contest, but the winner neither mated nor courted with the female during the 15-min test period; and type 3, where males held a contest and the winner then mated with or courted the female."

Restricting the analysis to type 3 interactions, the results showed that bigger spiders won more contests, but only if the difference was greater than 20 per cent of the larger spider's mass. "If the mass difference was due to a recent meal, then the larger spider never had an advantage, except when the difference was greater than 30 per cent."

Most interestingly, though, was the discovery that spiders could be trained as winners or losers. If the previous fight record of a spider is taken into account, it becomes clear that those who have lost several encounters tend to avoid future fights, while those that have a winning record are less likely to back down when faced with a potential rival. Their method of assessing whether or not to fight is based as much on their perception of their own fighting abilities as the size of their opponents.

But no one likes fighting just after a heavy meal.

Similar results were reported in "Assessment strategies in the contests of male crickets, Acheta domesticus (L.)" by Mace A Hack. The question was essentially whether male house crickets apply the lessons of game theory in identifying characteristics associated with fighting success and establishing an association between opponent asymmetry in these characteristics and the cost of picking a fight with them. As with spiders, the results showed that the heavier fighter tended to win, though with crickets it was also found to be an advantage holding the fight in your home burrow. Winners usually consumed more energy in the fights that losers, but generally speaking "the cumulative energetic costs of combat for both opponents increased with decreases in asymmetry of mass and energy expenditure rate". Which is clearly something all aggressive crickets ought to bear in mind before picking a fight.