To study the potential competitive risk of the introduced Chrysoperla carnea (Stephens) on the indigenous trash-carrying chrysopid Mallada desjardinsi (Navás), we studied the occurrence of cannibalism and intraguild predation (IGP) at different prey densities. In C. carnea, 100% cannibalism was observed in the absence of aphids. In M. desjardinsi, cannibalism was also observed, but absence of cannibalism occurred at 35% in pairs of second- third-instar larvae and at 70% in pairs of third- third-instar larvae. In pairs of M. desjardinsi larvae whose trash package had been artificially removed, all third-instar larvae ate second-instar larvae. The trash package may play a role in the reduced mortality of younger larvae by cannibalism. IGP occurred in all pairs. In the absence of aphids, the interaction was symmetric between second-instar larvae, but asymmetric for second- versus third- and third- versus third-instar larvae, and the interaction was similar when M. desjardinsi larvae with or without trash package were paired with C. carnea larvae. When third-instar larvae of both species were paired, C. carnea larvae ate significantly greater numbers of M. desjardinsi larvae than vice versa. The trash package of M. desjardinsi larvae may thus not play a defensive role against IGP by C. carnea. Increasing the availability of aphids tended to decrease both cannibalism and IGP levels. Nontarget effects such as competitive displacement resulting in loss of potentially beneficial attributes of the indigenous M. desjardinsi by the exotic C. carnea are likely to be negligible under conditions of abundant aphids.