Vinegar eel is a tiny roundworm that lives in vinegar. Vinegar eels are usually found in barrels or jars of nonpasteurized cider vinegar. They feed on fruit pulp and the bacteria that produce the vinegar from the cider. Vinegar eels are harmless when swallowed. The vinegar eel is slender and threadlike. They reach about 1/16 inch (1.6 millimeters) long. There are separate males and females. Most female vinegar eels live about 10 months. They produce as many as 45 tiny larvae (young), which are about 1/100 inch (0.25 millimeter) long.