This time of year I often see a bright, clear flash of yellow in the garden and know it is a wanderer, a Cloudless Sulphur butterfly. On my trip to some refuges down east earlier in the week I saw plenty of these vibrant yellow beauties as they are a common species in the coastal plain. They can be found statewide, especially in late summer and early fall, when they tend to migrate in large numbers northward and inland from the coast.
The primary host plant is Partridge Pea or Senna, a legume common in disturbed areas like roadsides and power lines throughout the eastern U.S. I learned the genus as Cassia 20+ years ago but it has since been reclassified (as have so many of the pants I struggled to learn in my state park days) as Chamaecrista fasciculata. Partridge Pea is a shrubby plant with loose bright yellow flowers and pinnately compound leaves.
The leaves close at night giving rise to another of its common names, Sleeping Plant. There is also a noticeable raised gland at the base of the petiole, although I did not find any reference as to the function.
The plant is also host for some other species of butterflies including the Orange Sulphur, Sleepy Orange, Little Yellow, and Gray Hairstreak.
The seeds are contained in a typical legume seed pod and are eaten by a variety of birds.
Eggs are minute and sculpted and laid on flower buds or leaves.
The caterpillars are brightly colored and I have seen them most often feeding on the flowers or flower buds, especially in the later instars.
When disturbed, the caterpillar will often drop from the plant and curl into a tight ball.
Their chrysalis is one of the most unusual and beautiful of any I have seen. It can be a variety of colors and is oddly elongated in two directions. Apparently, most of the Cloudless Sulphurs that migrate leave few, if any, offspring behind as the species tends to be intolerant of cold conditions so does not fare well far from the coastal plain. I plan to monitor this chrysalis and see its fate, although I am guessing a butterfly may emerge in a couple of weeks rather than the chrysalis overwintering.
The butterflies are said to nectar at a wide variety of plants but they seem to prefer red flowers in my garden, especially Coral Honeysuckle and Cardinal Flower. I may try throwing a few seed pods of their host plant along the edge of the garden this fall in the hopes of attracting even more of these dazzling fliers next season.