Spread out the black sugar on a small plate. Rub the lime wedge around the rim of a rocks glass; dip the glass in the black sugar, then fill with ice.
Combine the rum and lime juice in a cocktail shaker. Fill with ice and shake well. Carefully strain into the glass, minding the sugar on the rim. Top the drink with ginger beer and add the gummy spider.
Photograph by Kate Mathis
Recipe courtesy Claire Robinson for Food Network Magazine