I've never, personally, had a fighting conch attack anything living. Here's some insight on the fighting conch from ORA:
Florida Fighting Conch - Strombus alatus
The Florida Fighting Conch (pronounced "konk") is one of the most significant new items to be cultured for marine aquariums in years. This is due to the nature of this mollusk. It lives in the coral sand beds and eats algae such as diatoms. This makes the Fighting Conch the best live sand bed stirrer and cleaner on the market today. Fighting Conch are bred exclusively at ORA and their culture techniques were developed here.
Fighting Conch do not fight with anything in the aquarium, so it's a bit of a misleading name. The name derives from the fact that they partake in a ritualistic mating fight between males to determine sexual dominance. They do not disturb any reef tank inhabitants such as corals, clams, or other invertebrates. S. alatus only grow to about 3 inch size, so they will not "out-grow" the tank. ORA sells Fighting Conch at 1-1 1/2 inches. At this size they are "hermit crab proof", so small hermits cannot eat them and steal their shells.
Fighting Conch are known as herbivorous detritivores because they will eat both live and decaying vegetable matter. They will eat all algae growing on the surface of the live sand bed, and other detritus on the bottom. They prefer to stay in the sand and will slightly burrow, although not deep enough to disturb anaerobic areas deep in the sand.
Fighting Conch are more active at night, so they are less visible during the daytime. They can be additionally fed any algae derived food such as algae tabs, Tang diet and even sinking Koi sticks. If they are observed climbing up the glass of aquariums, this usually means they are hungry and should be fed.
ORA recommends that Fighting Conch be kept at a density of no more than 1 or 2 animals per square foot of sand bed. Higher densities may result in the conch out-competing each other for available food and some may starve.
