When spiders leave their family networks as they mature, it’s not because of their antisocial tendencies as previously speculated – rather, the adult’s subsequent isolation causes it to become intolerant of its former kin.

That’s according to new research with the solitary European labyrinth spider (Agelena labyrinthica), published in the journal PLOS Biology.

Many animals are only transiently social during their lifecycle and quickly become intolerant of others after isolation. This includes more than 48,000 species of spiders.

While spiderlings are known to be amicable towards each other, after venturing out on their own their behaviour becomes extremely aggressive and can escalate to cannibalism between siblings and mates or even infanticide.

Raphael Jeanson, from the University of Toulouse, France, and colleagues hoped to shed light on this under-researched phenomenon and better understand how to encourage permanent sociality – a trait accomplished by about 30 species of spiders.

In a series of experiments, they used a mixture of behavioural, chemical and modelling methods to explore why the spiders disperse and become aggressive.

The results showed that the spiders’ sociability did not decline when they remained in each other’s presence, and that dispersal occurred naturally with greater mobility, not as a result of decreased interaction.

Further findings confirmed the cannibalistic behaviour was a direct result of increased isolation. Even feeding the spiders did not mitigate the impact of social isolation on aggression, ruling out the potential role of starvation.

However, ready availability of prey did delay the spiders’ need to disperse. And, notably, extended connections helped to maintain sociable behaviour.

The aggression may result from a shift in the way spiderlings process chemical signals, and thus social cues, from their kin.

Jeanson says the findings reveal that “the mechanisms eliciting aggressiveness are much more sophisticated than previously thought”.

Importantly, he says, “Our study highlights the need for extended social interactions to preserve tolerance, which opens new perspectives for understanding the routes to permanent sociality.”