Last July I took this photo of a butterfly at the Montour Trail near Pittsburgh but even after searching BugGuide.net I could not identify it.

I got close.  I guessed it was a crescent, maybe a “northern crescent” but forgot to look up the species’ range.  Uh oh!  Range is important when identifying birds and even more important with butterflies.  Northern crescents are unlikely in southwestern Pennsylvania.

Field marks are important, too, but I didn’t have all of them.  My photo shows the upper side but the underside of a butterfly often holds the deciding field mark.

Puzzled, I emailed my butterfly friends Chuck Tague and Monica Miller.

Chuck told me that pearl and northern crescents look a lot alike but the location indicates this is a pearl crescent (Phyciodes tharos), not a northern.  Monica added that “My understanding is you really can only reliably tell them apart upon dissection and the northerns would only be found in places north of us like Buzzard Swamp.”

Wow.  These butterflies are as hard to tell apart as chickadees!  I’m glad I didn’t find this one in their overlapping range.

I’ve got quite a lot to learn about butterflies.  In the meantime I’m getting by with a little help from my friends.

Thank you, Chuck & Monica!

(photo by Kate St. John)