Rare Species Guide

  Synonyms

Speyeria idalia

  Basis for Listing

From the 1960s to the early 1990s the Regal Fritillary (Argynnis idalia) suffered a catastrophic decline in the eastern half of its historical range (NatureServe 2025). There is only one population of the eastern subspecies that remains extant (USFWS 2023). Populations in the western part of the range are better but have also declined more recently. 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; however, the rapidity and severity of the decline strongly suggests that the species is susceptible to subtle environmental change. Because of these range wide declines, the western subspecies of Regal Fritillary was federally listed as threatened in 2024.

In the western part of its range, including Minnesota, the Regal Fritillary is restricted to native prairie habitats (Debinski and Kelly 1998, NatureServe 2025). Approximately 18 million acres (7.3 million ha), in what is now Minnesota, was prairie at the beginning of Euro-American settlement, and this butterfly was undoubtedly common throughout all but the north end of the Red River valley (Prairie Parkland and Eastern Broadleaf Forest provinces), its northern range limit today. A little more than 1% of Minnesota's native prairie remains, fragmented into widely scattered, mostly small patches 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 spatially separate colonies linked by dispersal among them. 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 almost obliterating the 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. Difficulty in discriminating Regals from any of these species would only arise for individuals seen at a distance or for extremely flight-worn individuals. None of these other species has the striking contrast in coloration between the forewings and hind wings noted above.

  Habitat

In Minnesota, the Regal Fritillary is strongly associated with native prairie habitat. An occasional adult may be observed in non-prairie situations; however, these are dispersal events. Adults are encountered in both upland prairie and in wet prairie, though 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, typically only once, but appear to remain concealed in the vegetation for a period of several days after mating, becoming visibly active only after male numbers have greatly declined (Kopper et al. 2001). They visit flowers for nectar but do not begin laying eggs until late August (Wagner et al. 1997). They are capable of laying over 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 on violets (Viola spp.) exclusively. In Minnesota, the principal larval host appears to be the prairie violet (Viola pedatifida) of upland prairies; however, bird's foot violet (V. pedate var. pedata) is also used in southeastern Minnesota. It remains unknown to what extent the Regal Fritillary uses the stemless blue violets, primarily northern bog violet (V. nephrophylla) of damper prairie 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). That said, 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. Regal Fritillary larvae are likely to survive medium to low intensity fires (McCullough et al. 2017). Wherever practical, only a fraction of a site should be burned during a Regal Fritillary generational cycle, especially in sites that appear to be effectively cut off from immigration. Maintenance of sufficient unburned habitat through two or more successive seasons for an adequate reservoir of butterflies at a site is still important because some mortality is to be expected (Moranz et al. 2014). 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; however, it creates another, as hay raking could result in 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, though heavy, prolonged grazing eliminates the violet. Prairie reconstructions that lack acceptable violets will not support Regal Fritillary reproduction. Planting host plants in such reconstructions will create suitable habitat and can support reintroduced Regal Fritillary populations (Shepherd and Debinski 2005). 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,. Broadcast application of herbicides to control brush or invasive weeds such as leafy spurge (Euphorbia virgata), spotted knapweed (Centaurea stoebe subsp. micranthos), and Canada thistle (Cirsium arvense) may also reduce or eliminate both the larval host plants and 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. 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 occurrence records are entered in Biotics, a database maintained by the Minnesota DNR’s Natural Heritage Information System, 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 that are restricted to these remnants. The Minnesota DNR also aids 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.

  Authors/Revisions

Robert P. Dana, Ph.D. (MNDNR), 2025

(Note: all content ©MNDNR)

  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.