Each spring when the cleft phlox blooms and the oaks begin to leaf out in the sandy areas of Illinois, it’s time to search for the olympia marble. It flies from April until May (less than 30 days).
In Illinois, this diminutive beauty is locally encountered in sandy areas and dry hill prairies along the Mississippi and Illinois rivers. Its green-patterned caterpillar feeds on the flowering parts and seedpods of various rock cresses.
The falcate orangetip is one of the true harbingers of spring in southern Illinois, as it visits the blooms of spring ephemerals. Its green-patterned caterpillar feeds on the buds, flowers, and seedpods of rock and winter cresses as well as other mustards.
Watch for the falcate orangetip from mid-March to mid-May in moist, open, deciduous forests, especially those with young trees and plenty of small, open areas. It is rarely found north of Interstate 72 and is most common in southern Illinois.
Each spring the hoary elfin nestles into bearberry bushes on the Lake Michigan dunes in Lake County, taking flight when disturbed. Its range in Illinois is restricted to these dunes where bearberry, its caterpillar host plant, grows.
The adult can be found from April into May, but generally is only at peak numbers for a few days during that time span. The flight period varies each year, depending on the weather.
The frosted elfin is an unlikely sight in Illinois, since it has only been documented once in Lake County back in 1922. Illinois is at the extreme edge of its range (most records are from farther east).
This elusive species inhabits oak savannas and barrens that contain stands of lupine, its caterpillar host plant. The frosted elfin is on the wing from April into May—gone before the trees have fully leafed out—and would be easy to miss if a location is not checked regularly to catch its emergence.
Henry’s elfin comes and goes with the blooming of redbud—its caterpillar host plant—and by the time the blossoms are gone, so is the butterfly. Depending on the year, it can be found from late March into May, but an individual adult flies for only about a week.
Henry’s elfin is a forest species, often seen taking moisture at damp spots along woodland trails or darting around redbud blossoms. On occasion, it has been encountered on hill prairies, where it perches on red cedar, sometimes in the company of the olive hairstreak.
Look for Henry’s elfin in the southern two-thirds of the state—it has not been recorded north of I-80. It occurs commonly in the river valleys of west-central Illinois.
Eastern Pine Elfin
The eastern pine elfin makes its once-a-year appearance from April into May in forested areas with either native or planted pine stands. As the common name implies, the caterpillar feeds on various species of pine.
While a few scattered records occur from throughout Illinois, the eastern pine elfin is more commonly found in southern Illinois. The species is probably much more common than records indicate, but its habit of staying high in the tree canopy keeps its true distribution a secret.
The best chance to see it is to travel a trail or back road through pines in Pope County, usually in late April on a sunny day, after a rain. Watch puddles, and if anything flies up, pinpoint where it lands and carefully approach. This method should provide an opportunity to see the species.
The spring azure is one of the earliest butterflies to emerge from its chrysalis, with adults flying between late March and mid-May. It is a woodland butterfly, and is best sought in river valleys near stands of dogwood—the caterpillar host plant in Illinois. The adult visits flowers and damp spots.
The spring azure is more common and widespread south of State Route 136—only a few records occur from the northern counties. However, a reevaluation of specimens in collections is needed to determine the true distribution and status of the spring azure.
The dusky azure is a forest butterfly, prevalent before the trees leaf out in spring—from late March until mid-May. Look for it in deep, wooded, east-west running ravines, and on north-facing slopes, always near its caterpillar host, goat’s beard. Check goat’s beard blooms for the caterpillar—it is sometimes easier to locate than the adult.
The dusky azure is scattered and very localized across the state. While probably more widespread than records indicate, it will always be limited in numbers, uncommon, and difficult to locate due to its specific habitat requirements and short, early flight season.
The seldom-encountered silvery blue occurs in dry, open areas; oak savannas; and old railroad grades where its caterpillar host plant—veiny pea—occurs. The adult flies from April into mid-May, and is gone by the time most trees and shrubs leaf out.
The silvery blue is a rare species in Illinois—it occurs in localized colonies and is never widespread. With one exception, the species has only been found in the northeast corner of the state. The Chicago area has had known populations for over a century; the best of these occurs in the Palos Park area. A few additional viable populations are known in the northern tier of Illinois counties, from Winnebago to the east. Additional unknown Silvery Blue colonies may exist in that region, but the species' appearance in spring is so brief that it is easily missed.
A canopy-dwelling butterfly of oak forests, the northern hairstreak seldom reveals itself. Look for this species in the last two weeks of May along woodland edges or forest trails. It uses white oak, as well as other oaks, as caterpillar hosts.
The northern hairstreak is considered a rare, breeding resident and one of the least encountered species in Illinois. It appears sporadically and could be found anywhere in the state where oaks abound, but few records exist. This is likely due to the butterfly’s habits, more than its actual rarity, as it undoubtedly spends most of its life in the oak canopy.
To learn more about these species and other butterflies found in Illinois, check out Butterflies of Illinois: a field guide, available from University of Illinois Press.