By Carolyn Belardo
Chris Johnson was on the final task of his to-do list before the museum opened to the public when he stopped dead in his tracks.
“I thought: ‘Somebody’s fooling with me. It’s just too perfect,’” recalled Johnson. “Then I got goose bumps.”
What the volunteer in the Butterflies! exhibit at the Academy of Natural Sciences of Drexel University saw was an extremely unusual butterfly—emerged just hours before from its chrysalis—spreading its delicate wings wide to reveal that it was exactly half male and half female.
Its two right wings—brown with yellow and white spots—were characteristic of a female of the species, and its two left wings—darker with green, blue and purple coloring—were typical of a male. 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.
“It slowly opened up, and the wings were so dramatically different, it was immediately apparent what it was,” said Johnson, a retired chemical engineer from Swarthmore, Pa., who spotted the delicate creature one day in October as he was emptying the Butterflies! exhibit’s pupa chamber.
The pupa chamber is where exhibit staff place the chrysalises and cocoons that are shipped from overseas in order to allow the butterflies and moths inside to develop and emerge properly. Then they are released into the exhibit.
Johnson and his supervisor, Butterflies! Coordinator David Schloss, carefully isolated the butterfly and contacted Entomology Collection Manager Jason Weintraub, a lepidopterist. They knew it was important to save the butterfly for research by turning it over to Weintraub rather than let it loose in the exhibit, and run the risk of something happening to it during the handful of days it would live there.
Weintraub immediately confirmed Johnson’s suspicion. The butterfly was Lexias pardalis, and it had an unusual condition called bilateral gynandromorphy.
The Academy plans to put the butterfly specimen on public display for a limited time starting Saturday, Jan. 17.
What does it all mean?
“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.
This condition is extremely rare, but scientists don’t know just how rare it is because it is usually overlooked in most species where the two sexes look similar to one another.
So how did this unusual butterfly end up at the Academy?
This particular Lexias pardalis had been shipped in October as one pupa among many from a sustainable butterfly farm on Penang Island in Malaysia. Similar farms in Costa Rica, Kenya and the Philippines also keep the Butterflies! exhibit supplied with pupae that then transform into butterflies.
Lexias pardalis does not have a standard colloquial name, but it is a member of the butterfly family Nymphalidae, commonly known as “brush-footed” butterflies. Lexias butterflies live in tropical rainforests of Southeast Asia. The males sport iridescent black, greenish-blue wings, while females are larger and have brown wings with yellow and white spots.
What would Charles Darwin say?
Such differences in the sexes are the result of what Charles Darwin called sexual selection. They evolved over many thousands of generations as a result of “choosy” females. These butterflies use color and wing pattern as signals during courtship. The mates they select pass their traits on to the next generation.
Preserving the unusual specimen in the Entomology Collection provides scientists with an important source of information for the study of comparative morphology, anatomy and evolution—an important reason why natural history research collections such as the extensive ones at the Academy are so important.
Collecting insects from natural environments consistently from year to year also allows scientists to track how a population’s numbers rise and fall over time. They can understand how factors like climate change and environmental damage may be affecting insect populations.
Given the large size of the Academy’s Entomology Collection, which contains more than 3.5 million specimens, it’s very difficult to determine if it contains other gynandromorphic insect specimens, and
even more difficult to know how frequently they occur in nature.
“In most cases, such specimens are ‘discovered’ in museum collections by a researcher who is carefully examining reproductive organs of insects under the microscope and stumbles across a specimen with both male and female characteristics,” Weintraub said.
For Johnson, a naturalist and Academy volunteer for more than five years, his discovery was a thrill of a lifetime. “It’s something when you realize how special a phenomenon it is,” he said.
This special butterfly—preserved and pinned—will be on display at the Academy for visitors to see from Saturday, Jan. 17, through Monday, Feb. 16.
Read more about the rare butterfly in the following publications: