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U.S. Forest Service

Cloudless Sulphur Butterfly (Phoebis sennae)

By Evan Cole, Pollinator Partnership

Cloudless sulphur butterfly. Cloudless sulphur butterfly. Photo by Charles J Sharp [CC BY-SA 4.0], via Wikimedia Commons.

The sulphur butterfly, often known as the cloudless sulphur butterfly, is a large yellow butterfly found throughout most of the mainland United States. It is most common in the eastern United States and southern portions of the western United States, but it has been spotted as far north as Canada. Its genus name is derived from the name of the Greek god Apollo’s sister, Phoebe. Its species name is derived from the genus of its favorite host plants, Senna, a member of the pea family.

Sulphur butterflies have an average wingspan of about 2-3 inches. There is some sexual dimorphism between male and female sulphur butterflies. The males are typically solid yellow, while the females are yellow with a black border on their wings and a dark spot at the center of each forewing. Male sulphur butterflies also display some seasonal dimorphism. Winter forms are typically larger and have darker markings.

Adult female Phoebis sennae Adult female, Phoebis sennae, dorsal view. Photo by Donald Hall, University of Florida.

Adult male Phoebis sennae Adult male, Phoebis sennae, dorsal view. Photo by Donald Hall, University of Florida.

Before metamorphosing into an adult sulphur butterfly, the caterpillar feeds on leaves and flowers, especially those of the Senna and Cassia genus. Both Senna and Cassia are poisonous, which allows the caterpillars to accumulate a toxic deterrent to would-be predators. Unfortunately, this causes many farmers and gardeners to rip the plants out. The caterpillars are often considered elusive pests, because they turn green when eating green leaves and turn yellow when eating yellow flowers. Caterpillars grow thousands of times their hatchling size before pupating.

Green larva of the cloudless sulphur Green larva of the cloudless sulphur, Phoebis sennae (Linnaeus). The head is to the left. Photograph by Jerry Butler, University of Florida.

Adult butterflies are strongly attracted to red flowers, and have even been known to dive into the red lenses over car taillights. They have exceptionally long tongues that allow them to reach the nectar of even the longest and narrowest flowers. The adults are as clever at camouflage as their younger selves, typically resting on flowers that closely match the neon yellow color of their wings.

Sulphur butterflies exhibit migration and overwintering behavior similar to monarch butterflies, but they do not travel as far or in as great of numbers. During fall, sulphur butterflies abandon their breeding sites in the northern reaches of the United States and travel south to Florida and other parts of the southern United States There they reside until the end of winter when they can again return north to the same breeding sites as the year before. One of the greatest threats to these and other migrating butterflies is the destruction and loss of habitat caused by human development and improper environmental management. However, the vast range and relatively abundant populations of the sulphur butterfly suggest that this beautiful species is thriving and will be here for some time to come.

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