The Sensational Butterflies exhibition at the London Natural History Museum is usually an opportunity for experts to wow museum-goers about colorful butterflies from around the world. But at this year's exhibition, one unusual great Mormon butterfly surprised even the experts.
The butterfly is an extremely rare half-male, half-female bilateral Gynandromorph, which means that it appears to be male on one side but female on the other, according to the Guardian.
Dual-sex animals are a rare occurrence in nature, but it's especially rare for such a creature to be so uniformly bilateral. This butterfly appears perfectly split down the middle, with smoky black colors on its male side, but with visible flecks of blue, red and tortoiseshell on its female side. It also has one antenna longer than the other, a single male clasp on its abdomen, and its genitalia are also cut half and half — the male and female reproductive organs are fused right down the middle.
"It's an amazing butterfly. The split is purely bilateral — even the color of one side of its body is slightly different," said Luke Brown, manager of the Sensational Butterflies exhibit. "It has half-male, half-female sexual organs welded together. So they don't work; it is infertile."
Gynandromorphs form after sex chromosomes fail to properly separate during the division of a fertilized egg. Besides insects, other animals known to have been born with the condition include crabs, lobsters, spiders and even birds. The reason that bilateral Gynandromorphs are so rare is that this error must happen during one of the very first cell divisions to create an even split.
"Pure bilateral Gynandromorphs are incredibly rare, and I have only ever come across three in my whole career of 30 years," said Brown. "Many permanent butterfly exhibitions will go through their entire existence without ever seeing one of these rarities."
The butterfly has not shown any ill effects of its strange condition, and is flying well and feeding normally. Brown noted that there is no reason it shouldn't live just as long as other butterflies of its species.
Unfortunately for museum-goers, though, that lifespan lasts only about a month, so you'll have to scurry if you want to catch a glimpse of the Gynandromorph before it perishes. Until then, it will continue to be on display, merrily floating about at the Sensational Butterflies Exhibition, which runs through September.