The Intertwined Relationship between the Common Violet and the Great Spangled Fritillary
—By Vicki Bonk
A native plant gardener soon realizes there is infinitely more going on in their habitat plot, no matter how small, than readily meets the eye. Tuning into and connecting with garden life by noticing the variety of species, their relationships and habits at different times of day and season, we find ourselves more understanding of the interconnectedness of it all. If we pause to consider the life happening even in the common blue violet (Viola sororia) patch, we may be drawn to looking more closely, treading more softly, and gardening more carefully.
The relationship between violet and fritillary life cycles is but one case of what is not often readily noticed by the unpracticed eye in the native habitat garden. Taking the time to understand floral/faunal connectedness in nature has a double-fold benefit. First, we are more likely to witness more of what’s unfolding in a given habitat and second, by practicing awareness, we play a vital role in allowing natural space to be one where its inhabitants can survive and thrive.
I have been aware for years that the violet plant family (Violaceae) is the larval host plant of greater fritillary (genus Speyeria) butterflies. This awareness gave the “yard violets”—as the common blue are often called—and Canadian violets in my yard a pardon to meander freely. However, other than spotting fritillary butterflies nectaring on summer blooms, I had never seen evidence of the fritillary’s other life stages in my lush violet grounds.
Curious, I recently delved into the life cycle of the great spangled fritillary (Speyeria cybele), the fritillary seen most often in the Twin Cities area where I live. All lepidoptera (moths and butterflies) go through the process of metamorphosis that begins with an egg being laid, and then moves through the larva (caterpillar), pupa (cocoon or chrysalis), and adult (winged) phases. There are multiple variations in the way these stages manifest in lepidoptera, influenced by time of year, type of host plant, and the life cycles of both the insect and the plant. Such is the diversity of life: Multiple species are somehow able to live within their own niche, sharing an environment without getting in each other’s way.
The larval stage requires specific plants that the lepidoptera species has evolved to feed upon: the species’ host plant(s). Some lepidoptera are specialists, having only one host plant species they can feed upon, such as the well-known exclusive association of the monarch butterfly and milkweed. Others are generalists, having more plant species as a selection. The great spangled fritillary (as are all greater fritillaries) is a specialist reliant solely on violets to nourish its young.¹
Lepidoptera life cycles have evolved over thousands of years in tandem with the life cycle of its host plant(s), so there is critical “matching up” that must take place. Looking closely at the greater fritillary, we can start by examining its fascinating life cycle in early summer. Males emerge first from their chrysalides, usually a number of days before the females.
When the females emerge later, the mating begins. As is true of all the greater fritillaries, the great spangled are single brooded (one generation per year). After mating, the male’s life soon ends, while the females live on in a state of reproductive diapause.²
During July and August, the females are rarely seen and live in a somewhat dormant state, perhaps hidden in a woodland. It’s not until late summer that they become more active and visible. During this time, females deposit their creamy white eggs singly, near or on violets. When the tiny, black fuzz-ball caterpillars emerge, they eat part of their eggshell for sustenance. However, they do not eat any of their violet host plant at this time. Instead, the miniscule first instar caterpillar overwinters among the insulation of leaf litter.³
The nearly invisible fritillary caterpillars overwinter near or on violets. So note well: Late summer and early autumn are not the time to be thinning violets. Rather, a good time to thin spreading violets is in July and early August when the host plants aren’t occupied by eggs or caterpillars. Later in the season, fallen leaves will blanket these violets, providing shelter. Thus, we see a case for leaving the leaves alone. Leaves and duff offer necessary life cycle habitat.
With Mother Nature´s amazing co-evolutionary timing (that is, timing that has not been disturbed by the mismatches caused by climate change), the itzy-bitzy overwintering caterpillar becomes active in spring, usually May, right when violets begin to emerge. At this time, the larvae begin to ravenously munch on the violets’ delectable new growth. The great spangled fritillary life cycle is synchronized with the violet’s growth cycle in order to give these caterpillars an abundant supply of food. Again, gardeners are cautioned to let the leaf litter be for a myriad of ecological reasons. The great spangled fritillary is highly secretive and its spring survival relies heavily on fallen leaf cover. To avoid predators, larvae hide among the leaves during the day and come out at night to dine on the violets. No wonder we unaware humans rarely see them! Ground-feeding birds and spiders looking for a meal are among the most likely to detect these larvae.
Left undisturbed and uneaten, the caterpillar completes its instar stages sometime in June and pupates into a well-camouflaged and concealed chrysalis—suspended head downward by silken threads attached to a log, rock, bark or leaf. A few weeks later, the butterfly ecloses, and we’ve now come full circle with the great spangled fritillary life cycle.⁴
At this point, the native plant gardener can sustain the newly emerged butterfly by extending a floral welcome. Invite the adult butterflies in your landscape to stick around by providing the fritillary’s preferred native nectar plants: milkweeds, Joe Pyes, native thistles, coneflowers, wild bergamot, and more. Consider the “floral refreshments” of late summer bloomers so that female fritillaries can then notice that your garden also includes its necessary host plant, the violet. The more violets your garden offers, the more visible and viable it becomes as a food source for next season’s very hungry caterpillars.
Plentiful violets are essential for fritillaries, but their ecological usefulness reaches further. As a part of the circle of life, fritillary larvae are a food source for birds and other predators. And, native bee species such as mining bees (Andrena), mason bees (Hoplitis), bumble bees (Bombus) and sweat bees (Halictus) are all attracted to violets. Syrphid flies eat violet pollen, and skipper butterflies are attracted to the nectar. Some birds and small mammals find the seeds delectable. Ants consider the seeds an important food source, unintentionally farm them, leading to more violets! This spring-blooming ground cover has wonderful “bee lawn” characteristics: the pollen and nectar food source of a native plant, low growing, mowable, foot traffic tolerant, resilient, and perennial.
With their proliferation methods, violets can become too much of a good thing. There are ways to work alongside them. Edit violets only in July and early August to avoid editing the fritillaries. Keep violets working for wildlife (and you) in a number of ways. Allow them to be massed as a groundcover (that’s best for the fritillaries, too). Violets are manageable as a garden border, and as a pollinator lawn alternative when combined with other native plants such as self-heal and wild strawberries. Violets are a terrific living plant mulch/cover under shrubs. Violets can also be brought into check by having them share space with other “exuberant” plants such as ostrich fern. Violets also grow well underneath many trees, affording a soft landing environment for a variety of beneficial insect larvae, as well as providing better soil moisture retention.
Violets have a niche in the homegrown habitat garden. Diminishing wild areas make “bringing violets home” vital. Fritillary butterflies, who need violets to exist, have helped elevate violets from its misunderstood status as disrespected “yard violet” to a key host plant, reliable nectar plant, and a key ingredient in an alternative lawn. Understanding the ecological value of all native plants and their faunal relationships gives us inspiration and knowledge to act as engaged stewards. Even in one little patch at a time.
¹The fritillary family is comprised of the greater fritillaries (genus Speyeria) and the lesser fritillaries (genus Bolloria). Butterflies in the Speyeria genus cannot survive without a violet host plant. Butterflies in the Bolloria genus use violets as a host plant, although the native passionflower is also used as a host for several lesser fritillary species.
²Diapause in lepidoptera is a state of paused or suspended reproduction in which females do not mate or reproduce.
³Instar stages are the developmental stages between insect molting in which the exoskeleton is shed.
⁴ An insect ecloses when it emerges as an adult from a cocoon or chrysalis, or emerges as a first instar from an egg.