Out My Backdoor: Cloudless Sulphurs: Fall's Most Overlooked Migrant

By Terry W. Johnson

By the time autumn officially arrives, the fall migration of many migratory birds such as warblers, flycatchers and vireos has passed us by. However, during the ebb between when the last waves of early fall migrants bid Georgia ado and Jack Frost has transformed our countryside into a multihued tapestry of vibrant autumn colors, we have the opportunity to witness another migration: the migration of the cloudless sulphur butterfly.

Although the butterfly's passage is easy to see since it takes place during the daytime and passes through our backyards, most folks don't have any idea that these gossamer-winged beauties migrate. Right about now you might be wondering if you have ever seen a cloudless sulphur.

Chances are you have seen more than your share.

Cloudless sulphurs are fairly large, boasting wingspans of 2 ½ to 3 inches. Their underwings are greenish-yellow and have a number of small silvery spots. The butterfly gets its name for the fact that the topsides of its wings are bright lemon yellow and free of any markings.

When we think of butterfly migration, most of us conjure up images of monarchs making their way to their wintering grounds in Mexico. In truth, a number of other butterflies migrate. In addition to the cloudless sulphur, the list includes the red admiral, common buckeye, American lady and long-tailed skipper, to name a few. However, the cloudless sulphur displays the most spectacular of these seasonal movements.

In late summer, cloudless sulphurs from as far north as Canada begin moving southward. Using the sun to keep them on course, these large, showy yellow butterflies migrate only about 12 miles a day. Males tend to try to reach their wintering areas as quickly as possible. The migration of females, however, is more a leisurely affair. By moving more slowly, it is thought that they are able conserve valuable energy reserves needed in egg-laying.

During migration, cloudless sulphurs rarely stop long enough to feed. Their flight pattern is direct, as if they are on a mission that can't wait. In reality, they are.

Consequently, the cloudless sulphurs now feeding in your backyard probably haven't begun their migration. During migration, you are apt to see these bright-yellow butterflies in a host of places. They are regularly spotted in backyards as homeowners rake leaves, flitting down green fairways as golf balls arc overhead, drifting over malls and tall buildings in downtown Atlanta, or dashing above youth football games on sunny Saturday afternoons.

Most of these migrants are heading for their wintering grounds in south Florida and beyond. Entries in the journals of both Christopher Columbus and Charles Darwin describe clouds of sulphurs seen on their voyages. One is left wondering if these were indeed cloudless sulphurs winging their way across the ocean. Although I have not seen cloudless sulphurs out over the ocean, I have found thousands washed ashore on Sapelo Island, the apparent victims of capricious winds.

For reasons we don't fully understand, while millions of cloudless sulphurs are flying south from late summer to fall, smaller numbers of cloudless sulphurs are making their way north. Most of these butterflies face the promise of certain death once freezing weather arrives.
Cloudless sulphurs overwinter as adults. Although they are more cold-hardy than many butterflies, only a few try to overwinter in North and Middle Georgia. During the majority of the time, they remain inactive in sheltered areas. But they can be seen flying about on warm winter days.

Once spring bursts forth, cloudless sulphurs begin migrating north. However, the northward migration is but a shadow of the spectacular fall migration.

As the butterflies fly north, they lay eggs on partridge pea, sicklepod senna and other closely related plants. When a new generation of cloudless sulphurs emerges from the eggs, many of these butterflies head northward. By the end of the summer, populations are prospering as far north as southern Canada.

This helps explain why cloudless sulphurs were scarce this year throughout much of the state, but by September they were one our most commonly seen butterflies.

Two of the nectar plants that, in my experience, cloudless sulphurs seem to prefer at this time of year are Turk's cap and pineapple sage. Both have bright red blooms that act like cloudless sulphur magnets. Other late-blooming plants that are great sources of nectar for resident and migrating butterflies in your yard include goldenrod, aster, swamp sunflower, liatris (blazing star), zinnia and salvia.

The next time you spot a cloudless sulphur visiting flowers in your backyard, stop and enjoy the butterfly's beauty and reflect on the perilous journey that awaits this seemingly fragile creature.

It is a backyard moment worth savoring.

Terry Johnson is a former Nongame program manager with the Georgia Wildlife Resources Division, a noted writer and expert on backyard wildlife, and executive director of TERN, the friends group for Wildlife Resources' Nongame Conservation Section.