A new study led by a team from Southern Medical University in Guangzhou, China, shows that bumblebees not only show a more "optimistic" judgment tendency after experiencing pleasant events, but this internal positive state can also be transmitted to their peers through visual interaction in just about 30 seconds of social contact, forming an effect similar to "emotional contagion" in the entire colony.
The research object was the common white-tailed bumblebee (Bombus terrestris). The researchers first trained individual bees to learn to distinguish two colors: one color represents a sugary reward, and the other represents no reward. After this association was formed, the experimental team introduced an intermediate fuzzy color between the two to examine the response speed and tendency of bees in "uncertain situations." This so-called "judgment bias test" is widely used to measure how animals interpret ambiguous cues in optimistic or pessimistic emotional states.
The results show that when bees are in a more positive internal state, they will approach these ambiguous colors faster, as if they are "expecting good things to happen"; while individuals in a bad mood or in a lower positive state will act slowly or even simply avoid these uncertain signals, thus providing a very sensitive behavioral baseline for subsequent identification of "emotional shifts".
After establishing the baseline, the research team arranged a key link: providing a "demonstration bee" with a small drop of sucrose as a reward, and then allowing the bee that had enjoyed the sweet reward to have social contact with another "observer bee" that had not received the reward for about 30 seconds. The experimental environment excluded external cues such as smell and color. The observer bee could not "copy" by imitating foraging cues. The only information available was the other's significantly active body movements and behavioral performance after receiving the reward.
Subsequently, the researchers conducted the same judgment bias test on these observation bees, and found that these bees that had not tasted the sugar water in person, when faced with the ambiguous color, showed a similar quick approach behavior to the "in-person winners", as if they had experienced good things. This change was regarded by the research team as a positive "emotional shift" in the internal emotional state, rather than just a brief excitement or simple social imitation.
In order to eliminate other possible factors, the team designed a control experiment: when the same brief contact was carried out in a completely dark environment, the two bees could still contact and touch each other, but could not see each other. In this case, the subsequent judgment behavior of the observing bees did not show any significant change in optimism, indicating that it is difficult to explain this phenomenon through channels such as touch or smell. The real key is the visual perception of the active actions of the "demonstration bee".
Research leader Peng Fei said that what surprised the team most was that this "optimistic contagion" occurred so quickly. Just one social contact lasting about half a minute was enough to change the observation pattern of uncertain cues after observing the bees. This means that the internal state of bees can be indirectly "regulated" by peers in a very short time without sharing food or communicating through clear signals.
Previous studies have proven that bees themselves can swing between positive or negative states, and this work further shows that this internal state is not just at the individual level, but can spread through social interactions in the group, which gives people a more detailed understanding of the bumble bee group behavior and social adaptation mechanism.
At the mechanistic level, although the research team did not directly measure changes in neurotransmitters in the bees, they pointed out that the behavioral patterns of the observed bees after brief contact were highly similar to the tendency of insects to be more optimistic about ambiguous cues when experimentally increasing dopamine levels. Therefore, it is speculated that the regulation of dopamine-related reward pathways may be involved behind this "visual contagion", but the specific neural mechanisms still need to be further verified through neurobiological means in the future.
This research also raises an equally important reverse question: Since positive internal states can spread rapidly among bees, is it possible that negative states such as disturbance, stress, etc., spread in a similar way among bees? The researchers pointed out that if this assumption is true, then in artificial management or agricultural utilization scenarios, bee colony welfare is not just "hard indicators" such as feed, nutrition, and disease control. Creating an environment as low-pressure and quiet as possible may also be a key factor in maintaining the overall health and efficiency of the bee colony.
Overall, this study published in the journal Science shows that bumblebees are able to convey an internal state similar to "positive emotions" to their companions through only brief visual contact. This adds a new layer to the understanding of insect social behavior and reminds people that even small animals may have much richer instant experiences and internal worlds than the traditional impression of "mechanical instinctive reactions".
The research team's next plan will focus on further revealing the neural basis and physiological pathways of this emotional "contagion", including the roles played by different brain regions in it, and the spatiotemporal scale of the spread of these internal states in the group, so as to more fully explain why interactions of just tens of seconds can leave lasting traces at the behavioral level.
The researchers are still cautious to avoid directly equating this phenomenon with "happiness" or "joy" in the human sense, but this work undoubtedly challenges the stereotype that "insects are just instinctive machines" and shows that even tiny animals like bees have internal states that can influence and shape each other. These invisible psychological processes are quietly involved in building the daily life and social structure of the bee colony.