in earthworms, the clitellum can only be seen when the worm is sexually mature. it may be white, orange-red or reddish-brown in colour. earthworms are ready to mate when their clitellum is orange. in leeches, the clitellum appears seasonally. its color is usually slightly lighter than that of the body of the annelid. occasionally, living segments of the worm will be shed with the clitellum.