Enlarge / Orange amphipods caught the eye (and interest) of Brown University graduate students conducting field research. (credit: David Johnson) Scour the salt marshes of Plum Island Estuary in Massachusetts and you're likely to spot bright orange shrimp lurking among the vegetation and detritus. That unusual hue is a sign that a shrimp has been infected with a parasitic worm, which also seems to affect the shrimp's behavior.