A museum exhibit volunteer at the Drexel University in Philadelphia, Pennsylvania, one day “got goose bumps” last fall when he stumbled upon a strange butterfly, which was half male and half female.

Chris Johnson, a volunteer for the university's Academy of Natural Sciences, was preparing for next day’s exhibit called “Butterflies!” in October when he spotted the rare butterfly, emerging from its chrysalis and slowly spreading its wings to reveal its unusual traits. The butterfly, which was found to be Lexias pardalis, will be displayed at Drexel's Academy of Natural Sciences from Jan. 17 to Feb. 16.

“It slowly opened up, and the wings were so dramatically different, it was immediately apparent what it was,” Johnson, a retired chemical engineer from Swarthmore, said in a statement. “I thought: Somebody’s fooling with me. It’s just too perfect."

The butterfly’s two right wings were brown with yellow and white spots, which are the characteristics of the female species. Its two left wings, on the other hand, were comparatively darker with green, blue and purple marks, which are the distinctive features found on a male butterfly.

“The right wings were shaped differently than the left wings, and the body’s coloration was exactly split lengthwise down the middle as half male and half female,” according to the statement.

In order to preserve the butterfly for further research, Johnson handed it over to Entomology Collection Manager and lepidopterist Jason Weintraub, who subsequently confirmed that the insect had an unusual condition called “bilateral gynandromorphy.”

“Gynandromorphism is most frequently noticed in bird and butterfly species where the two sexes have very different coloration. 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,” Weintraub said.

Gynandromorphism is considered to be extremely rare, but scientists are yet to determine how rare it is because the condition is overlooked in most species where the two sexes look similar to each other.

The butterfly that Johnson discovered had been shipped in October along with other butterflies from a Penang Island farm in Malaysia.