Fair disclosure: I've never seen one of these rare butterflies in real life. They have no economic significance, but they're certainly distinctive, and people who live near them love them. They are the official state butterfly emblem of Arkansas. My interest in the Diana Fritillary is academic. It's another butterfly that, merely because it's large, gets mistaken for the Monarch butterfly. A site called Answers.com disgraced itself by displaying the answer that female Monarch butterflies are blue. They're not. But female Diana Fritillaries are.
I put one picture of a male and one of a female "Diana" on objects in the "Save The Butterflies" collection at Zazzle. I had to pay for them in wasted time, annoyance, and junkmail. Because of the Fair Use Rule I can use different pictures here. (When this web site was Amazon-affiliated we didn't gank photos under the Fair Use Rule. Now we can.)
The male Speyeria diana has dark brown wings with deep yellow borders. Individuals vary but his wingspan is typically a little less than four inches. He is larger and darker than most of the "closely related" species, but his coloring is typical of the group called fritillaries. (They're called fritillaries in honor of medieval church officials, who were also called fritillaries, who wore yellow-orange robes, just as cardinals wore bright red robes.)
The female has iridescent black wings with icy blue borders. Her wingspan is typically a little more than four inches.
The undersides of her hind wings are dark drab, without the spots and spangles fritillaries usually have. She looks less like a typical fritillary than like a big dark swallowtail, possibly the toxic Pipevine Swallowtail. Birds are motivated to leave her alone.
True gender confusion can happen in this species, although it's rare. The Smithsonian Institution has preserved a specimen of a Diana with male-type wings on one side and female-type wings on the other.
Did it fly? "Perfect specimens" in museums were often reared in cages and killed before they had a chance to fly.
Fritillaries are both pollinators and composters. Dianas are often found sipping flower nectar but they may also be found savoring the mineral salts in fresh dung.
Caterpillars start out as small dark bristly things and develop into large dark bristly things that try to look like some sort of cross between a stingingworm and a centipede. However, their bristles don't contain venom and only make the caterpillars harder for predators to bite. Violet leaves are edible and these caterpillars aren't as toxic as they benefit from predators thinking they are.
There are two generations of Dianas each year. The winter caterpillars actually hatch in autumn and spend the winter hidden at the roots of violet plants. They are shell eaters with an instinct to eat their own shed skins, which discourages predators and also tends to limit populations. Videos of shell-eating caterpillars' behavior when several are crowded together gives a misleading impression. In nature these animals are not crowded together. Female butterflies spend most of their lives flying about looking for fresh places to lay their eggs where no caterpillar will ever meet a sibling. They have no social instincts whatsoever. When they come to a skin of their kind of caterpillar, they eat it. When they find the skin occupied by another living caterpillar they don't know what to do, but one of them will usually end up eating the other. They are not cannibals by choice; they have to be artificially crowded together, away from their natural food, to become cannibals. But this is the way nature protects many large butterflies and moths from overpopulating and destroying their food supply.
Dianas have always been rare but used to be more widespread than they are now. In the nineteenth century they were found near the Mississippi River and in the Northern States. In the twentieth century they've been fairly well confined to the Southern mountains. Sightings in Virginia's Blue Ridge Mountains seem to be on the eastern side of the mountains, not the western side; I have a large patch of the blue-and-white violets they're thought to like best, but populations of this species on my side of the mountains have been extirpated and no Dianas ever take advantage of my violets. This species is badly threatened by land "development." They need unsprayed, unpolluted, somewhat shady fields where violets grow in abundance, to survive.
Though Dianas and Monarchs use food plants that grow in different conditions, in nature they may use different parts of the same fields. Milkweeds grow further from adjacent woods or woodlots; violets grow near and under the trees. Both species will benefit when people choose to leave unsprayed, mostly undisturbed green spaces for "butterfly gardens."
A final fun fact: Speyeria diana was an official name long before Diana Spencer's icy blue eyes became famous. Big, showy butterfly species were often named after characters in ancient literature, where Diana was the goddess of wild things--the moon, forests, animals, hunting, and what little the ancient world knew about conservation.
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