There are 3.5 million specimens in Drexel University's Academy of Natural Sciences entymology collection, and a few months ago, a volunteer spotted a butterfly there that is truly one in a million.
The butterfly, known as Lexias pardalis, had half its body covered in markings typical of the male of its species and half covered in female markings. "I thought: 'Somebody's fooling with me. It's just too perfect,'" said Chris Johnson, the volunteer who made the discovery while working on the Academy's Butterflies! exhibit. "Then I got goosebumps."
"It slowly opened up, and the wings were so dramatically different, it was immediately apparent what it was," he added, according to a statement about the discovery released Tuesday by Drexel.
What Johnson had stumbled upon as he was cleaning out the exhibit's pupa chamber -- the place where butterflies burst forth from their chrysalises -- was a Lexias pardalis with a rare condition known as bilateral gynandromorphy.
"Gynandromorphism is most frequently noticed in bird and butterfly species where the two sexes have very different coloration," said Jason Weintraub, the Academy's entomology-collection manager. "It can result from non-disjunction of sex chromosomes, an error that sometimes occurs during the division of chromosomes at a very early stage of development."
The rare butterfly came to the Academy from a sustainable butterfly farm on Malaysia's Penang island. Its right side exhibits the coloration typically displayed by females -- brown with yellow and white spots. Its left side shows the male markings -- iridescent black and greenish blue wings.
The butterfly, which has the short lifespan common to all of its kind, has been preserved and pinned and will be on display for visitors at the Academy from January 17 through February 16.