Nathan Brockman, Reiman Gardens
This leopard lacewing butterfly is half female, half male, as its colors clearly show.
updated 5/31/2011 3:05:14 PM ET 2011-05-31T19:05:14

In April 2004, James Adams found an unusual tiger swallowtail butterfly. One side was nearly black, with signature blue and orange markings on the lower wing. The insect's other wing, however, sported a bright yellow. For a collector of butterflies and moths it was a rare find: a gynandromorph, a dual-sex creature.

A gynandromorph's body is part male, part female. In the most spectacular cases, called bilateral gynandromorphs, each sex gets half of the insect: wings, genitalia, body size and other sex-related features.

Adams found the tiger swallowtail at Pigeon Mountain in northwest Georgia, but the location doesn’t really matter, the professor of biology at Dalton State College in Georgia said.

James K. Adams, Professor of Biology, Dalton State College
The dual-sex tiger swallowtail butterfly that James Adams found.

"You never go out to look for those because they are genetic anomalies," Adams said, "you happen upon them."

Often nearly invisible
The first of these dual-sex insects he found was a forest tent caterpillar moth on the wall of a gas station underneath a light. This one was less spectacular, but more typical of the many gynandromorphs that may go unrecognized. A line down the middle of its body marks the division between the lighter, somewhat fluffier male side and the longer female side; the difference in length causes the abdomen to curl.

Gynandromorphy isn't unique to butterflies and moths; he-she bees, lobsters, spiders and crabs have been found, to name a few. But among many species males and females look alike, making for much less visually interesting gynandromorphs. This also makes it difficult to estimate their true frequency.

How to make a gynander
Among some insects, as in humans, sex is determined by a set of two chromosomes. For us, two X chromosomes means female, and an X and a Y means male.

James K. Adams, Professor of Biology, Dalton State College
This unassuming forest tent caterpillar moth is both male and female.

An insect can become a gynandromorph if the sex chromosomes do not properly separate during the first division of a fertilized egg. Because of this mistake, one of the resulting cells, and its descendants, end up with too many chromosomes while the other side gets too few. Depending on the chromosome code used by the species, these mismatched sets can read as male or female, resulting in an insect that has male cells in some parts of its body and female cells in others. An error later during development can result in the mosaic variety, in which patches of the body are male while others are female.

In addition, insect gynandromorphs can arise when an egg with two sex chromosomes, instead of the normal one, gets fertilized by two sperm. A symbiotic bacterial infection has also been linked to gynandromorphs in some insects, such as wasps, according research published in March 2010 in the journal Terrestrial Arthropod Reviews.

This particular sexual aberration is not believed to be possible for humans and mammals, because of the way our sex characteristics are determined, but it has been found among birds.

And how to lose one
Perhaps the most literary of insect gynandromorphs belonged to the Russian novelist Vladimir Nabokov, who studied and collected butterflies and moths.

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In his autobiography, "Speak, Memory: An Autobiography Revisited" (Vintage, 1989), he recounts a childhood memory of his governess sitting upon his prized specimens, smashing them. He writes: "A precious gynandromorph, left side male, right side female whose abdomen could not be traced and whose wings had come off, was lost forever: one might reattach the wings, but one could not prove that all four belong to that headless thorax on its bent pin."

You can follow LiveSciencewriter Wynne Parry on Twitter @Wynne_Parry. Follow LiveScience for the latest in science news and discoveries on Twitter @livescience and on Facebook.

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Explainer: Top 10 oddballs of the animal world

  • Image: Platypus
    Healesville Sanctuary

    From the outside, the platypus looks like a grade-school art project assembled by a kid too busy making spitballs to pay attention in class. The creature, which is classified as a mammal, has a duck's bill and webbed feet, lays eggs like a reptile, but has fur and rears its young on milk.

    Researchers say the platypus genome is equally cobbled together from bird, reptile and mammalian lineages. One more oddity: Males can deliver venom from tiny spurs on each hind limb. Click on the "Next" arrow above to learn about nine more oddballs in the animal world.

    More info: Mixed-up platypus genome unscrambled

    — By John Roach, contributor

  • Colossal squid has plate-sized eye


    In April 2008, scientists in New Zealand looked a thawing colossal squid in the eye and discovered that the eye is, well, colossal — about the size of a dinner plate. That makes it the largest animal eye on Earth. Fishermen caught the 1,000-pound creature last year in Antarctic waters and froze it intact for scientific study. Colossal squids can reach 46 feet in length and have tentacles equipped with suckers and hooks. Scientists believe the creatures can descend to 6,500 feet and are active, aggressive hunters.

    More info: Huge squid caught, could be biggest ever

  • Aye-aye gives grubs the finger

    Duke University Lemur Center

    The aye-aye is a bushy-tailed primate from Madagascar with big eyes and bat ears. But call it funny-looking and it just might extend its extra-long middle finger in your general direction. The member of the lemur family otherwise uses the extended digit to fish out grubs from the crevices of trees. Captive aye-ayes such as the one shown here from Duke University are teaching scientists about the evolution of color vision.

    Learn more about the brainiac of all lemurs

  • Star-nosed mole sniffs out food, fast

    Image: Star-nosed mole
    Kenneth C. Catania / Vanderbilt

    The fleshy appendages that ring the snout of the star-nosed mole, shown here, make it one strange-looking creature. But when it comes to eating, those 22 tentacles help the mole detect and devour food faster than the human eye can follow — in a fraction of a second. Researchers say the speedy feeding allows the mole to prey on small insect larvae that would otherwise be too energetically costly to eat. The creature lives and forages under the cover of marshes and wetlands along the east coast of North America.

  • Burrowing toad is genetically different

    Robert Puschendorf

    For an amphibian, the stocky and squat Mexican burrowing toad doesn't look all that strange, but it's actually unique. A global conservation program called EDGE of Existence ranks the toad as the most "evolutionarily distinct" amphibian in the world. A fruit bat, polar bear, killer whale, kangaroo and human are all more closely related to one another than the toad is to any other species, according to the program. The Mexican burrowing toad, as its name suggests, spends most of the year underground, coming out only after particularly heavy rains to breed in pools of water.

    Learn about other bizarre amphibians under threat

  • Yeti crab lurks on the ocean bottom

    A Fifis  /  AP

    Named after the legendary shaggy man-beast that tromps through the snows in some of the world's tallest mountains, the Yeti crab blindly scurries about hydrothermal vents along a ridge at the bottom of the Pacific Ocean. First observed in 2005, the crab, officially named Kiwa hirsute, sports a carpet of pale yellow hairs on its arms. Scientists suspect the crab uses those hairs either to farm bacteria or to feel its way around the seafloor for food and potential mates.

    More info: Scientists to list all species on Web

  • Narwhals, the 'unicorn' whales

    Glenn Williams / Harvard Medical School

    Unicorns are purely mythical creatures, but the myths may have been inspired by narwhals. Most males and some females among the 2,200- to 3,500-pound whales sport an 8-foot-long appendage that emerges from the left side of their upper jaw. Scientists recently discovered that the elongated tooth is packed with nerve endings, making it extraordinarily sensitive. The whales may use it to determine the salinity of water and search for food. Male narwhals are also known to rub their tusks together, presumably because it gives off a unique sensation.

    More info: Mystery of 'unicorn' whale solved

  • Sucker-footed bats stick to Madagascar

    Field Museum (left); Bat Conservation Int'l (right)

    In January 2007, scientists announced the discovery of a new species of bat that uses suckers on its thumbs and hind feet to stick to broad-leafed plants such as the traveler's palm. The new species, Myzopoda schliemanni (left image), was found on the dry, western side of the African island nation of Madagascar and is closely related to another sucker-footed bat called Myzopoda aurita (right image) that lives in the humid eastern forests. Conservationists were heartened by the discovery because it suggests the bats can adapt to pioneering broad-leafed plants in deforested areas. Only about 8 percent of the island's original forest cover remains.

    Watch NBC video: What's killing all the bats?

  • Long-eared jerboa hops onto the screen

    Image: Long-eared jerboa

    In December 2007, conservationists released the first known footage of an endangered rodent they've nicknamed the "Mickey Mouse of the Desert." Known more formally as the long-eared jerboa, the little critter has ears about one-third larger than its head, and legs that allow for hopping like a kangaroo. The International Union for Conservation of Nature lists the species as endangered. One threat: the domestic cat.

    More info: Mongolian 'Mickey Mouse' caught on tape

  • Ligers, wholphins and grolar bears, oh my!

    Image: Liger
    TODAY show

    Every now and again, trysts between two different species result in oddball offspring that capture the public's fascination. Ligers, which are a cross between a male lion and a female tiger, were immortalized in the 2004 cult movie "Napoleon Dynamite": The main character of the 2004 cult movie, played by Jon Heder, describes it as "pretty much my favorite animal." (A real one is shown above.) Other popular hybrids include wholphins, which are a cross between false killer whales and Atlantic bottlenose dolphins; and the "grolar bear," a cross between a grizzly bear and polar bear.

    Watch NBC video of a liger
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