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Speyeria idalia, Regal Fritilliary

Adult Speyria idalia feeding on nectar

Speyeria idalia Drury was first described as a species in 1773. This nymphalid butterfly has a wingspan of 6.7 to 10.5 cm and is considered a strong flier. Originally, the regal fritillary ranged from Maine to Montana and south to North Carolina and Oklahoma. Today, several larger populations occur in the Great Plains states; few, fragmented populations occur in the Midwest; and two isolated populations occur in the east, in Pennsylvania and Virginia.

The regal fritillary can be found in xeric tallgrass prairie habitat in the west and in damp meadows and wet fields in the east. Adults emerge in June/July and can be seen through September. Adults feed on nectar from milkweeds, thistles, red clover and mint. Females are highly fecund, laying up to 2,500 eggs each in late August. Interestingly, females do not orient egg laying to violets, which are believed to be the larval food plant. Instead, they oviposit using a “sweepstakes” strategy, where they spread many eggs over a variety of microsites on the underside of dead vegetation in varying degrees of grass/forb overstory shade. This helps to maximize reproductive potential in the face of climatic variance. Caterpillars emerge in the fall and overwinter. They do not begin feeding until the spring, when violets emerge, specifically Viola pedata and Viola pedalifida. These nocturnal-feeding larvae are black and yellow with short, branching, spiny hairs.

The reasons for S. idalia decline are numerous and controversial. Habitat loss and fragmentation have greatly affected the species. Captive populations have failed due to a virus that may also be active in the wild. Pesticides may play a role, as they have coincided with sharp declines of S. idalia in the last 40 years. Regal fritillaries are currently listed as a Federal Species of Concern; and both the species as a whole and the controversial eastern subspecies are being petitioned for listing as endangered species.

The two eastern populations both occur on military facilities. The Fort Indiantown Gap Military Reservation in PA is home to 500 to 1000 regal fritillaries each year, with about 300 acres of fritillary habitat. Due to habitat destruction caused by tank training and aerial bombing, the North American Butterfly Association filed a lawsuit in 1998 against the Army and National Guard to save this butterfly. Today, the Department of Defense allocates $250,000 to $300,000 annually to manage the Fort Indiantown Gap population. A Nature Conservancy manager is present on-site to help the managing practices, which have included removal of woody and invasive plants and the planting of 25 acres of additional habitat.

In Virginia, mark-recapture studies are being conducted to assess the size of the population at the Radford Army Ammunition Plant. This population was only recently discovered in 1998 and not much is known about it. Unfortunately, the base has 44 sites that are contaminated by potentially harmful chemicals that threaten the nearby New River, and the clean-up efforts may be detrimental to the regal fritillary.


State of Missouri Endangered Species Guide Sheet - Regal Fritilliary

Written by: Joshua Grinath, 2004

Image © Missouri Conservation Commission. All rights reserved.