The term refers to corruption among grassroots officials, some of whom have been exposed by the ongoing anti-graft drive to be involved in huge illegal rackets. Their ranks may have been low, invariably below the level of county head, but the public funds they have embezzled or the bribes they have taken are no less than some senior officials.

In the house of Ma Chaoqun, director of a State-owned drinking water supply company in Beidaihe, Hebei province, investigators found more than 100 million yuan ($17 million) in cash, 37 kilograms of gold and ownership certificates of 68 houses in many cities, including in Beijing.

In fact, the harm caused by corrupt grassroots officials is no less than that by senior officials. Village and county heads, as well as directors of local branches of some State-owned enterprises, are in charge of implementing most of the policies and plans passed by the higher authorities. They are usually the distributors and users of many funds, and control important resources that concern the livelihoods of ordinary people.

All these make catching the "flies" (lower level corrupt officials) more difficult than catching the tigers (high-ranking corrupt officials). But the authorities have to take up the challenge and succeed.