FILE – A spider is seen on a flower. New research published in PLOS Biology found that adult spiders seem to forget how to behave with each other after being alone too long, which causes them to become aggressive. VOA
A friendly start in life
Baby spiders, known as spiderlings, begin their lives cozied up to their siblings — sometimes as many as several hundred. But when they grow up, they tend to live alone. Of the more than 40,000 known spider species, all but 30 lead solitary lives in adulthood.
It's not clear why so few spider species remain social their whole lives. Many researchers believe that spiders become more aggressive as they grow, which drives them to avoid each other. Chiara decided to test which comes first: aggressive behavior or social isolation.
Chiara and team members Felipe Ramon Portugal and Raphael Jeanson studied labyrinth spiders, which are common in France. They observed that baby labyrinth spiders started to move away from each other five days after emerging from their eggs, which the researchers initially thought pointed to a natural increase in aggression.
However, they found that even spiderlings raised alone started to move around more after five days. In other words, the spiders weren't fleeing from their siblings because they were worried they'd get eaten, they were just stretching their (many) legs and becoming more mobile as they grew.
If an increase in aggressive behavior doesn't happen naturally as the spiders age, something must cause it. To test this, the researchers raised some spiders alone and others in groups. They then brought together pairs of spiders that weren't familiar with each other to see if they reacted peacefully or violently.
Spiders that were raised in groups almost never tried to eat the unfamiliar spider, but those raised alone went on the attack 40% of the time. The more time they had spent alone, the more likely they were to try to eat the unfamiliar spider. The researchers concluded that isolation causes spiders to become aggressive and not the other way around.