June Nature Almanac: Variegated Fritillaries Invade Foothills Grasslands
By Stephen Jones, with Ruth Carol Cushman and Scott Severs
June 2022
When does a vagrant summer butterfly become one of our most abundant species? More often than we might think.
For years we've been seeing scattered numbers of variegated fritillaries--striking orange, black, and buff butterflies with an affinity for southern climes--in foothills meadows and plains grasslands. Not able to survive our cold winters during any stage of their life cycle, these agile fliers disperse northward each summer from permanent breeding areas in the southern United States and Mexico.
The common name describes the varied orange, buff, and white patterns on their underwings. No two individuals look exactly alike. Photo by Stephen Jones.
Until recently most butterfly observers characterized this movement as a one-way dispersal rather than a true migration. Recent research using stable isotope analysis indicates that some late-summer and fall-emerging variegated fritillaries do, indeed, fly south from the United States to Mexico. Road-killed individuals collected near Monterrey, Mexico, contained radioactive deuterium traceable to rainwater that had fallen on places of the butterflies' emergence throughout the central and eastern United States. (Read a report on the study or read the full study).
The common name variegated fritillary describes the complex pattern of orange, brown, and buff scaling on the underwings. The scientific name Euptoieta claudia derives from a Greek word for "easily frightened," reflecting this wandering butterfly's low, erratic flight, useful in evading predators.
Variegated fritillaries range from Argentina clear up into southern Canada, mostly from the Rocky Mountains eastward (map of North American range from Nature Serve). Host plants include passion vines, violets, pansies, purslanes, and flaxes. The 2-inch-long caterpillar has an orange body marked by black stripes, white spots, and branching, non-poisonous spines. The porcelain-like chrysalis is greenish-white with glistening gold bumps and black spots.
Their striking chrisalids have been compared to "porcelain jewel boxes." Photo by Sara Bright.
During the late nineteenth century, these fritillaries were considered rare in the northern United States. Early butterfly lists for Massachusetts categorized them as "strays," and prior to 1900 only a half-dozen sightings had been reported throughout that state. However, butterfly lists from Arizona, Colorado, and Wyoming eastward to New Jersey and Florida now tend to characterize this species as fairly common, and individuals have been reported within all the provinces in southern Canada.
Three years ago, Anyll Markevich, Christel Markevich, and I initiated a study of the impacts of cheatgrass infestation on mammals, birds, and butterflies on two Boulder County Open Space properties in the lower foothills south of Lyons. During the first spring and summer, fully 66% of all the butterflies we counted were variegated fritillaries. In fact, we counted more than 500 during a single two-hour survey.
Excited and astonished, we spread the word of a potential record breakout year for this species in eastern Colorado. Various other observers reported seeing lots of these fritillaries, but nothing approaching our numbers.
That fall, the Cal-Wood Fire raged through our study sites, scorching four of our eight study plots. The following spring and summer we repeated the surveys, and to our amazement found a nearly identical number of variegated fritillaries, again comprising 66% of all the butterflies we counted. So it appears that these wandering beauties may be much more abundant in Boulder County, especially in foothills grasslands, than previously thought.
At this point, we have no way of knowing what percentage of our late-summer-emerging variegated fritillaries will die off with the first hard freeze and what percentage will migrate successfully to warmer regions. But either way, as global temperatures continue to rise, the combination of seasonal dispersal and true migration will enable these wide-ranging butterflies to keep expanding their North American breeding range.
Variegated fritillaries perch low to the ground in grasslands and mountain meadows. Despite their skittish reputation, if you take a couple of quiet minutes to let them know you're a non-predatory human, they'll sometimes let you approach to within a few feet. Photo by Stephen Jones.
Other June Nature Events
Fritillaries in the genus Speyeria, including Aphrodite, northwestern, Edwards's, coronis, callipe, and Mormon fritillary, emerge from chrysalids in foothills canyons and mountain meadows to sip nectar from wild bergamot and other flowers. In late June and July, hundreds of Aphrodites and northwesterns emerge in upper Gregory Canyon; and in September, dozens of Mormon fritillaries sometimes appear at Fourth of July meadow above Eldora. Nearly all will lay their eggs on violets, the favored host plant for species in this genus.
Golden Eagle chicks mature and prepare to fledge from cliff nests in foothills and high mountain canyons.
Elk calves and mule deer fawns are born, and bighorn lambing begins.
The first Colorado columbines appear in mountain canyons and meadows.
Hackberry emperor butterflies mate and lay their eggs on their namesake host plant in dry, foothills canyons. This exquisitely patterned butterfly, cinnamon-brown on top and buff below with striking blue eyespots, is identifiable by touch; the males brush our bare arms ever so lightly as they gather sweat to nourish their sperm. After lapping up our sweat, they become easily approachable.
Hackberry emperor. Photo by Stephen Jones