A new study done at the University of Pittsburgh has found that there is a social species of spider that seems to utilize personality traits, rather than physical attributes like size, in order to decide who does what job. Among the Anelosimus studiosus, tasks like building the nest and rearing the young are delegated based on what seem to be behavioral tendencies.
It has already been well-established that for most social insects, size is a determining factor for work assignments. In ant colonies, the big ants provide the protection for the smaller worker ants. In the findings for this study, however, jobs definitely seem to be decided by personality traits.
The communal, social spider used for this study is Anelosimus studiosus. The researchers discovered that the females possessed two opposite and distinct personality types. Without any obvious links to different physical attributes, some females were aggressive and others were docile. When duties such as capturing prey were done, the aggressive spiders had much more success than did the docile ones. The aggressive females were also three times more liable to respond in cases of attacks by intruders. The researchers also noted that the communal webs built by the docile spiders were much smaller than those built by the aggressive females.
The scientists asked if this meant that the docile female spiders were basically freeloading off of the hard work of the aggressive ones. They then asked themselves how that could be effective for what seems to be a successful colony.
Their answers came when they found that the docile females were exceptional nannies. While the aggressive individuals were building, hunting and fighting, the docile ones were busy rearing the babies. Colin Wright, one of the researchers, said that finding out that the docile females were the daycare providers was the piece to their puzzle that had been missing. He also said that science now knows that the organizing of colonies can be done successfully using personality traits. This was previously thought to only be possible within species that had customized physical structures.
The authors do acknowledge that there could very well be underlying differences that lead to the personality traits observed, such as nervous system variances. They have simply noted that no observable physical differences were present.
They also pointed out that the definition of the word “personality” used is specific to the spiders and not what would normally be associated with the complicated world of human behavior. The researchers defined the spiders’ personality traits as “consistent variation in individual behavior across contexts.” This simply means that the spider will respond in the same way at all times, never showing a tendency to switch from docile to aggressive and back again, the way some humans do.
For the spider species Anelosimus studiosus, the fixed personality trait is a huge benefit. The researchers said that this mixing of traits made for a more successful colony than those with primarily one personality type. The same can be said of humans. This study has shown that, like men and women, personalities and behaviors are deciding factors in what kind of work these social spiders do.
By Stacy Lamy