Daphnia exhibits diverse morphological,behavioral and life-history responses to the kairomones of predators.A 10-day simulated experiment was conducted on anti-predation reaction of Daphnia similis,a dominant species in Lake Taihu,to invertebrate predator Chaoborus larvae.The experiment had three treatments: the presence of Chaoborus larvae (CL),control without Chaoborus larvae or filtered water (CK) and no Chaoborus larvae but with the filtered water that had cultured Chaoborus larvae the day before (FL).The results showed that the average body length,average number of offspring and cumulative number of offspring of D.similis in the CL and FL treatments were significantly higher than those in the CK treatment,which suggested that the release of kairomones from Chaoborus larvae can alter the life history traits of D.similis.These alterations can reduce the predation risk of D.similis.Our results indicate that invertebrate predator can affect the cladoceran population through both direct predation and release of the kairomones in the field.