Shell-boring predation is well-studied in the prosobranch gastropods, including representatives of the Naticidae (Carriker, 1981; Kabat, 1990), Muricidae (Carriker, 1981), Buccinidae (Peterson & Black, 1995), Marginellidae (Ponder & Taylor, 1992; Taylor, 1998), and Cassidae (Hughes & Hughes, 1981). In contrast, representatives of the Nassariidae had not been found to bore into shells until Morton & Chan (1997) presented the first evidence of shell-boring predation by Nassarius festivus juveniles. Representatives of the Nassariidae are considered to be “the closest attempt of an obligate scavenging life style,” although members, including Bullia digitalis and Ilyanassa obsoleta, eat live prey (Britton & Morton, 1994). The findings of Morton & Chan (1997) were intriguing because the N. festivus adults are not shell borers, but scavengers, which descend readily and speedily on fresh carrion (Morton & Yuen, 2000), whereas the juveniles bore holes and cannibalize their siblings. Offspring cannibalism of viable siblings in the study of trophic eggs has attracted much attention in such diverse taxa as sharks, nonsocial insects, frogs, spiders, and prosobranch gastropods (reviewed by Perry & Roitberg, 2006). For example, the sea whelk Hemifusus tuba feeds on trophic eggs, resulting in only a mean of 8.8 emerged as juveniles from a mean of 1,500 eggs laid in each capsule (Morton, 1987). Relatively little information is available on the gastropod juveniles that cannibalize similar-sized siblings. The aim of the present study is to provide empirical evidence of sibling cannibalism in N. festivus juveniles. The findings of Morton & Chan (1997) were obtained in a wholly accidental manner; some newly metamorphosed N. festivus left over an extended public holiday were dead and had their shells bored. The present study also answers the question of whether cannibalism was invoked by hunger. MALACOLOGIA, 2010, 52(1): 157−161