If you live in the southern U.S., you might find yourself face to face with bean leaf rollers (Urbanus proteus). These little caterpillars are common in home gardens, where they attack many members of the bean family.
What Is A Bean Leaf Roller?
Bean leaf rollers are the larvae of a species of skipper butterfly. The wingspan of adult butterflies measures as wide as 2 inches across, and they have long “tails” extending from their hind wings, making them look as if they’re trailing a pair of threads as they flitter about the garden. The butterflies are brown and nondescript; most gardeners might not even take notice of them. Their larvae, however, are hard to miss.
Bean leaf rollers are found in the southern U.S. They’re very common in Florida, Georgia and South Carolina, and they are sometimes found throughout parts of the Southwest, as well. They don’t survive freezing temperatures, so it’s rare to see these garden pests in areas where winters are cold.
Adult females lay yellow eggs on the lower surface of bean leaves. The eggs hatch a few days later. The larvae are small yellowish-green caterpillars with a dark, pronounced head. As the caterpillar grows, yellow lines develop along the length of its body.
To protect itself, each larvae notches out a piece of the leaf margin and folds the cut leaf piece over its body to protect itself from predators.
When the caterpillar is ready to pupate, it takes shelter in the leaf roll and forms a chrysalis. Pupation takes 1 to 3 weeks, depending on the weather and other factors.
Although Florida is thought to be the only state where these insects live year-round, they do migrate northward during the summer months. South Carolina gardeners might see them only very late in the season. Come fall, the adults migrate southward again, to escape the pending colder temperatures.
Bean Leaf Roller Damage
Bean leaf rollers feed at night, when they leave the protective housing of their leaf shelter. During the day, you’ll find them only inside their pieces of curled leaf. Their nocturnal feeding causes notches in the leaf margins. Only severe infestations causes significant damage.
What To Do About Bean Leaf Rollers
Typically, in home gardens, there’s no need to take action against bean leaf rollers because bean plants are fairly tolerant of the insect’s feeding damage. If you have just a handful of the larvae on your plants, let them be. But if they’ve consumed a significant amount of foliage, you can hand-squish the caterpillars while they’re inside their leaf shelters. There are many natural predators of bean leaf rollers as well, including spined soldier bugs and parasitic wasps. Spinosad-based organic insecticides work to control the larvae, though they are seldom called for.