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In addition to being a predator to several marine organisms, the Portuguese Man of War is prey for some other marine organisms.  One such predator is the Pacific sand crab found in Hawaii which has been known to capture men of war that have drifted into shallow waters.  The sand crab tries to drag the man of war into the sand, but the float is often pushed onto shore by the waves.  While hanging on to the float, the crab will roll up onto the beach.  The crabs seem to be unaffected by the nematocysts.

Nudibranch mollusks from the family Glaucidae are also known to feed on Physalia physalis.  The man of war is important not just as a food source, but also as a means of defense.  After ingesting the man of war, the nematocysts are used by the nudibranchs in their own bodies for defense.

Other predators of the Portuguese Man of War include Loggerhead and Leatherback sea turtles.  Unfortunately, due to improper trash disposal, these turtles sometimes mistake plastic bags for the man of war.  After ingesting the indigestable plastic bags, the turtles can get sick and die. 

Some Portuguese men of war also engage in symbiotic relationships with different fish species.  One such species, Nomeus gronorii, lives among the tentacles of Physalia and feeds on the tentacles while avoiding the nematocyst containg dactylozooids.  While the fish is not completely immune to the man of war’s stings, it can tolerate much stronger venoms than other fish and relies on agility and speed to keep from being stung.  In addition to the tentacles, the fish can feed on leftovers from the meals taken by the man of war.  The fish also receives protection from other predators while swimming amongst the tentacles.  The Portuguese man of war is not harmed because it can regenerate the tentacles and also benefits from using Nomeus gronorii as a lure to attract other prey to its net of tentacles.