Monday, June 29, 2015

Edwards' Hairstreak Census

The Edwards’ Hairstreak butterfly is one of the Blue Jay Barrens rarities that has been the target of many of my management activities.  Each year, in late June, I take a day to search the property for this small butterfly.  Things have changed considerably since I first found the species here more than 25 years ago.

Edwards’ Hairstreaks are strongly attracted to the orange flowers of the Butterflyweed.  Fortunately, the blooming season for this plant coincides exactly with the flight period of the butterfly.  As part of my search, I check every Butterflyweed I can find.  Last year I was impressed to find many flowers with two Hairstreaks visiting at once.  This year there were frequently three butterflies per flower head. 

Not every Butterflyweed had an attending Edwards’ Hairstreak.  The butterflies stay in close proximity to their larva food plant, Blackjack Oak.  I have been doing what I can to encourage the growth of Blackjack Oak in the fields and now have these oaks growing in several places that they had not been before.  In each of these areas, I’m now finding the Edwards’ Hairstreak butterflies.

This is the original site of the Edwards’ Hairstreak at Blue Jay Barrens.  Even here, the population size has increased through the years.  The caterpillars are generally found on the small, three to six feet tall trees.  Fortunately for the butterflies, the harsh growing conditions in this shallow soil causes the trees to die back during dry years, so the trees tend to stay perpetually short.

The butterflies are also found on and around the oaks.  Females will lay their eggs in the rough bark of the older branches of the tree.  So far, my efforts to photograph the egg laying process have been unrewarded.

Eggs hatch early in the spring and the caterpillars begin feeding on the tender, newly emerging leaves.  Later on, they feed on the larger leaves.  The evidence of their feeding remains through the summer. 

Male Edwards’ Hairstreaks select a courtship territory that they defend against other males.  Typically the territory centers around an oak that is suitable for receiving eggs.  Females entering the territory are pursued by the male in an effort to mate.  Butterfly numbers are trending upward and the territory they occupy continues to increase.  I like to think of these increases are indicators of the success of my management efforts.

I’ve included a short video of a male taking off from an oak leaf to chase away an intruder.  There were so many males in close proximity that a chase by one caused an encroachment on another’s territory, so there were often several individuals involved in the chase.  This video can also be viewed on YouTube by clicking HERE.


  1. Thank you! I have been trying to improve my small yard to bring in birds and butterflies. This is the first year a hummingbird and one monarch have been seen in the yard. After 5 years of work I am exceedingly happy to see them! Hopefully more next year with luck :)

    1. Hi, Renee. You should put a video on your YouTube channel so I can see what your yard is like.