At the American Museum of Natural History a rare butterfly was recently hatched, a pure bilateral gynandromorph or a butterfly that is half female and half male, which can be seen in the physical differences of its coloring. This is caused when the "sex chromosomes do not properly separate during division of a fertilized egg. Bilateral gynandromorphy results if this error occurs during the first cell division, resulting in an insect that has male cells on one side and female cells on the other.If such errors occur later in development, the gynandromorphy is mosaic and the separation into the two sexes isn't so clearly defined. Gynandromorphy can also occur when an egg with two sex chromosomes, instead of the normal one, gets fertilized by two sperm." While occurring withing various species such as spiders and crabs, gynandromorphy is very unusual and Luke Brown, the butterfly house manager has only come across 3 in his entire career of 30 years.
Out of the 4.5 million butterflies at the Museum (there are approximately 20,000 species of butterflies worldwide) only 200 are gynandromorphs. The butterfly above is a great mormon or Papilio memnon from Asia and when it dies it will be added to the Museum's collection for continued study, and with many species of butterflies either still undiscovered or lacking a scientific name that are often threatened by extinction.