One of the most striking butterflies flying about our backyards at this time of the year is the cloudless sulphur.  Although they have been patrolling our yards for months, they are definitely more abundant and approachable in the late summer and fall than they are at any other time of the year.  However, have you ever had the impression some of these midsize bright yellow butterflies are appreciably larger? 

      If you have, you may be happy to know that you are not seeing an optical illusion.  The truth of the matter is right now some cloudless sulphurs are significantly bigger.  It seems females remain the same size throughout the year.  However, such is not the case with the males.  They are what lepidopterist call seasonally dimorphic.  This is because they take on a different appearance in the fall and winter.  During this time of the year these butterflies have darker markings and are truly larger than males that emerged earlier in the year.