In the early days of Emperor Wu of Han's reign, with the Rebellion of the Seven Kingdoms still fresh in memory, court officials frequently debated the power of regional princes, arguing that their territories were too vast and their strength too great, and that their lands should be gradually reduced and their influence weakened, while they also deliberately exposed the princes' faults before the emperor. The princes, however, felt they were the emperor's own flesh and blood, yet now, whether guilty or innocent, they suffered insults from low-ranking ministers, and some government offices were nitpicking over trivial flaws, leaving them both furious and deeply worried.
In the third year of Emperor Wu of Han's reign (under the era name Jianyuan), the kings of Dai, Changsha, Zhongshan, and Jichuan came to the capital to pay homage. Emperor Wu hosted a grand banquet with music, where the melodies shifted from lively and joyful to subtle and sorrowful. His elder brother, Liu Sheng, the King of Zhongshan, was moved to tears by the mournful strains. When Emperor Wu asked why he wept, Liu Sheng replied, "I have heard that a sorrowful heart finds even a sigh unbearable, just as Gao Jianli's mournful zither at Yishui made Jing Ke unable to swallow his food. My own grief has long been pent up, and hearing such delicate music, tears now fill my eyes unbidden."
Emperor Wu of Han asked Liu Sheng what troubled him. Liu Sheng replied, "The spittle of many can float a mountain; the buzzing of countless mosquitoes sounds like thunder. Confucius was trapped in Chen and Cai because of the multitude. As the saying goes, 'Public opinion can melt metal, accumulated slander can dissolve bone.' I live far from the capital in Zhongshan, with few friends at court to spread my virtues, yet many speak ill of me. This worries me, and I weep. Now, due to the ministers' talk, my kin are estranged, and brotherly bonds dissolve like ice. The Book of Songs says, 'My heart is pained, as if pounded with a pestle!' That is my feeling." Liu Sheng then detailed the officials' encroachments on the princes to the emperor.
When Emperor Wu of Han heard Liu Sheng's words, he could not bear to use force against the princes, so he decreed that each prince could divide his lands among his own sons, letting them carve up their territories themselves, thereby gradually weakening their power.
The idiom "a swarm of mosquitoes makes thunder" means that when many mosquitoes gather, their buzzing sounds like thunder. It is a metaphor for how small things, when combined, can create great power.
Source: *Book of Han*, "Biography of the Prince of Zhongshan"
Meaning of the Idiom: Later, the Chinese idiom "聚蚊成雷" came to describe how small things when combined can create great power.