Rare Species Guide

  Synonyms

Speyeria idalia

  Basis for Listing

The regal fritillary has suffered a catastrophic recent decline in the eastern half of its historical range, from Wisconsin and Illinois east to the Atlantic seaboard. In the eastern part of its range, it is presumed extirpated in many states and is possibly extirpated in most of the remainder, as well as in Ontario. In the few states in this part of its range where it is still extant, it is either imperiled or critically imperiled (NatureServe 2008). It is faring better in the western half of its range, but it is considered apparently secure only in Kansas. In four states (including Minnesota) it is considered vulnerable, and it is imperiled or critically imperiled in the rest (NatureServe 2008). Because the decline in the east is not understood, it is not possible to evaluate the likelihood of this decline spreading to the western part of the range, but the rapidity and severity of the decline strongly suggests that the species is susceptible to subtle environmental change.

In the western part of its range, the regal fritillary is restricted to native prairie habitats (Debinski and Kelly 1998). Less than 1% of Minnesota's native prairie remains, and this consists of widely scattered, mostly small fragments surrounded by agriculture and development. Only a few of these remnants are large enough that they could support persistent populations if completely isolated, and probably none is large enough to provide an indefinitely secure future for a completely isolated population. The survival of the regal fritillary in Minnesota probably depends upon concentrations of remnants within the dispersal capabilities of adults that can collectively support larger populations. For these reasons, the regal fritillary was listed as a special concern species in Minnesota in 1996.

  Description

The regal fritillary is a large, distinctively marked species and one of temperate North America's most striking butterflies. Forewing length in males is 3.5-4.8 cm (1.4-1.9 in.). Females are slightly larger than males, with a forewing length of 5 cm (2 in.) not unusual. The sexes are similar in color and pattern. Above, the forewings are a rich reddish orange with a number of irregularly shaped black spots and a row of small whitish flecks in a narrow black border along the outer margin. The upper side of the hind wings is a somewhat iridescent blue black, with an inner row of large white spots and an outer row of smaller spots that are orange in males and white in females. The underside of the hind wings is identical in both sexes: a bold pattern of large, triangular silver spots in a dark brown ground color. The only butterflies in Minnesota that resemble the regal fritillary are the monarch (Danaus plexippus), the great spangled fritillary (Argynnis cybele), and the Aphrodite fritillary (A. aphrodite). A fourth similar fritillary, the Atlantis fritillary (A. atlantis), is restricted to the forested northern part of the state and wouldn't be encountered with the regal. Uncertainty of identification for any of the 4 species would only arise for individuals seen at a distance or for extremely flight-worn individuals. None of these has the strong contrast in coloration between the forewings and hind wings above.

  Habitat

In Minnesota the regal fritillary is strongly associated with native prairie habitat. Adults are encountered in both upland prairies and in wet prairies, although larval development may be restricted to upland prairie.

  Biology / Life History

The regal fritillary has a single annual generation. Eggs are laid in late summer and hatch after a few weeks. The tiny larvae do not feed after hatching, but hide in the duff and enter dormancy until the following spring, when feeding and growth begin. Larvae complete their growth in June and pupate, with emergence of adults beginning in mid-June and continuing into July. Males emerge on average a week or more before females and quickly begin searching for newly emerged females. Females mate soon after emergence but appear to remain concealed in the vegetation for a period of several days after mating, becoming active only after male numbers have greatly declined (Kopper et al. 2001). They visit flowers but may not begin egg laying until August. Females rarely mate more than once; they are capable of laying up to 1,000 eggs, which are matured gradually and placed singly, not in clusters or masses. Adult life expectancy in the wild has not been reliably determined, but individuals have been observed to survive a month or more (Nagel et al. 1991). Throughout their adult lives, both sexes feed frequently on floral nectar.

Larvae feed only on violets (Viola spp.). In Minnesota, the principal larval host appears to be the prairie bird's-foot violet (Viola palmata var. pedatifida) of upland prairies, but bird's-foot violet (V. pedata) is also used in southeastern Minnesota. It remains unknown to what extent the regal fritillary uses the stemless blue violets (primarily V. nephrophylla) of damper prairies in Minnesota. During the course of its development, a larva feeds on several violet plants consuming only a few leaves of each before moving to a new plant. Violet plants are dispersed in the prairie, and larvae probably have no means of finding plants other than by chance encounter. Thus the density of violets is a critical factor for successful development (Kelly and Debinski 1998).

Regal fritillary adults are powerful fliers capable of ranging widely across the landscape. However, little is known about their dispersal behavior. Adults are rarely encountered away from native prairie remnants, and they appear to have a strong tendency to remain within the boundaries of these (Ries and Debinski 2001). However, adults are frequently observed in remnants too small to produce self-sustaining populations, suggesting that dispersal among remnants is common.

  Conservation / Management

Frequent fire was an integral part of the prairie landscape, and prescribed burning is an important tool in managing the remnants to prevent woody succession and to help control invasive non-natives. However, burns probably cause high mortality in all immature stages of the regal fritillary (Swengel 1998). Wherever practical, only a fraction of a site should be burned during a butterfly generational cycle, especially in sites that appear to be effectively cut off from immigration. It is unknown whether females will lay eggs in prairie the first growing season after a burn when there is little or no duff; until it is determined that they do, care must be taken to maintain enough unburned habitat through two or more successive seasons to maintain an adequate reservoir of butterflies in a site. Haying can be a useful complement to prescribed burning in sites where constraints on burning would make it difficult to achieve management objectives with fire alone. It is not known whether females will lay eggs in a recently mowed prairie. Delaying mowing until most egg laying has occurred would remove this concern, but it creates another, as hay raking could result in significant larval mortality. Haying only part of a site each year is therefore advisable.

How the density of host-plant violets is affected by various prairie-management practices, such as burning, haying, and grazing, is not documented. In more mesic sites, the dense, tall stands of the dominant grasses that result from prescribed burning alone may reduce violet abundance. Light to moderate episodic grazing may stimulate violet reproduction, although heavy, prolonged grazing eliminates the violet. Prairie reconstructions that lack acceptable violets will not support regal fritillary reproduction; research is underway to determine if planting host plants in such reconstructions will create suitable habitat. Adults need plentiful sources of nectar. Intact prairies, with their high plant diversity, typically supply an abundance of good nectar flowers, which is enhanced following dormant-season burns. Grazing and mowing during the butterfly's flight period will reduce flower abundance, perhaps enough to force adults to emigrate from the site. Broadcast application of herbicides to control brush or invasive weeds such as leafy spurge (Euphorbia virgata), spotted knapweed (Centaurea maculosa), and several thistles may also reduce or eliminate both the larval host plants and many of the adult nectar sources.

Movement of adults among sites is probably important for the persistence of the regal fritillary in most prairie remnants in Minnesota. Many of the smaller remnants are unprotected and are likely to eventually vanish. This could lead to the disappearance of the regal fritillary from many of the surviving prairies. The decreasing likelihood of dispersers finding suitable opportunities for reproduction could exacerbate gene selection against dispersal. Even the largest prairies in Minnesota cannot support populations of this butterfly that are large enough to be secure against possible catastrophic events. Research that will permit modeling of the spatial dynamics of regal fritillary populations in Minnesota is needed.

  Conservation Efforts in Minnesota

Several survey efforts in Minnesota have included the regal fritillary as one of their target species. Documented occurrences are recorded in the Rare Features Database maintained by the Natural Heritage and Nongame Research Program, and these data are consulted in environmental review of projects that could affect the species or its habitat. Many prairie sites that support this species are protected and managed to maintain the prairie community by the Minnesota DNR, the U.S. Fish and Wildlife Service, and The Nature Conservancy. Land managers have been provided with guidance on the importance of subdividing sites and burning the units in a rotation that reduces the likelihood of extirpating insects and other small animals restricted to these remnants. The Minnesota DNR also provides assistance to private landowners in managing native prairie on their land. The Native Prairie Bank Program, the Native Prairie Tax Exemption Program, and a prairie restoration handbook are available to land managers and landowners to help protect and manage remaining prairie parcels.

  References and Additional Information

Debinski, D. M., and Kelly, L. 1998. Decline of Iowa populations of the Regal Fritillary (Speyeria idalia) Drury. Journal of the Iowa Academy of Science 105:16-22.

Henderson, R. A., J. Meunier, and N. S. Holoubek. 2018. Disentangling effects of fire, habitat, and climate on an endangered prairie-specialist butterfly. Biological Conservation 218:41-48.

Kelly, L., and D. M. Debinski. 1998. Relationship of host plant density to size and abundance of the Regal Fritillary Speyeria idalia Drury (Nymphalidae). Journal of the Lepidopterists' Society 52:262-276.

Kopper, B. J., S. Shu, R. E. Charlton, and S. B. Ramaswamy. 2001. Evidence for reproductive diapause in the Fritillary Speyeria idalia (Lepidoptera: Nymphalidae). Annals of the Entomological Society of America 94:427-432.

Nagel, H. G., T. Nightengale, and N. Dankert. 1991. Regal Fritillary butterfly population estimation and natural history on Rowe Sanctuary, Nebraska. Prairie Naturalist 23:145-152.

NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. . Accessed 9 June 2008.

Ries, L., and D. M. Debinski. 2001. Butterfly responses to habitat edges in the highly fragmented prairies of central Iowa. Journal of Animal Ecology 70:840-852.

Swengel, A. B. 1997. Habitat associations of sympatric violet-feeding fritillaries (Euptoieta, Speyeria, Boloria) (Lepidoptera: Nymphalidae) in tallgrass prairie. Great Lakes Entomologist 30:1-18.

Swengel, A. B. 1998. Effects of management on butterfly abundance in tallgrass prairie and pine barrens. Biological Conservation 83(1):77-89.