Via Ariely, this great experiment on the social facilitation effect from the 60’s: cockroaches do better on simple tasks in the presence of other cockroaches, but worse in the presence of other cockroaches when the task is difficult:
However, research by Zajonc, Heingartner, and Herman (1969) argued that such conscious, cognitive processes weren’t necessarily an important component, as cockroaches, which presumably do not have the same conscious processes as humans, showed the same social facilitation effect.
In this same experiment, Zajonc and colleagues also found that the cockroach’s performance decreased in the presence of other cockroaches when the task was particularly difficult. In the landmark article, “Social facilitation”, Robert Zajonc offered the theoretical explanation that the presence of others increases physiological arousal. During this state of arousal, he argued that performance increases when task is easy or familiar, while performance decreases when a task is difficult or unknown. As such, social facilitation effects came to be understood based on two components: the presence of others and the ease of the task for the individual.
I’d love to link to the original article, but it is locked up in some Elsevier safe somewhere, despite being a classic article that is at this point over forty years old.