Many Texans will tell you one of the strangest sights in early spring is the appearance of many small, wriggling, wormlike creatures that seem to have bungee jumped from tree branches.
“Some of those squiggly caterpillars dangling by silken threads, primarily from oak trees, are called oak leaf rollers,” said Wizzie Brown, Texas A&M AgriLife Extension Service entomologist, Travis County. “They typically show up throughout Central Texas over a stretch of several weeks during early to mid-spring”
In the larval stage, oak leaf rollers are creamy white to greenish color and have a dark brown or black head capsule. They have six legs and no prolegs, or false legs, toward the end of the abdomen. While they are no danger to humans, if left unattended these insects can potentially do harm to oaks and other trees that harbor them.
“It’s typical that in early spring there are a number of species of caterpillar, including the oak leaf roller, that will defoliate oaks and other trees,” Brown said. “Caterpillars feed on the early spring growth of trees and, from time to time, can eat most or all of their newly emerged leaves.”
Brown said other similar insects that may be prevalent during this time of year include spring cankerworms, which also dangle from a silken thread, and forest tent caterpillars.
Oak leaf roller moths lay their eggs on twig tips and leaf buds of several different tree species, where the eggs remain for about 10 months. Once the eggs begin to hatch, usually sometime in March, the caterpillar larvae begin to feed on tender new spring growth.
“Trees with heavy leaf roller infestations can potentially be partly or completely defoliated by mid- to late-April, which is when the fully grown caterpillars usually begin their pupal stage,” Brown said.
Oak leaf roller pupae are usually found on the tips of twigs, in bark crevices or on weeds and other plants growing near infested trees.
“When trees become defoliated by pests during the growing season, this creates additional stress on the tree and makes it susceptible to serious damage,” Brown said. “That’s because leaves provide sugar, which is later converted through photosynthesis into other carbohydrates. This allows the tree to grow and thrive, so large numbers of these insects damaging or destroying these leaves can have a serious negative impact on the tree.”
Controlling the rollers
Caterpillar pest outbreaks occur in cycles and rarely regularly occur year after year, Brown said. However, when they do occur in residential areas, valuable landscape or orchard trees may need to be protected from such outbreaks.
“If you have trees you know to have had past infestations of leaf rollers, be sure to watch them carefully,” Brown said. “At that time, if you see a fairly heavy defoliation, the tree can be sprayed with a registered insecticide labeled for that use.”
Brown said some potentially useful insecticides would be those containing Bacillus thuringiensis variety, such as kurstaki, spinosad azadirachtin, as well as other products labeled for controlling caterpillars on ornamental trees and shrubs.
However, she noted, in areas where large numbers of trees are clumped relatively close together, the use of insecticides for control of oak leaf rollers is simply not practical.
“Often, it’s best to just leave them alone and do nothing,” she said. “Post oak trees have survived in South and Central Texas without human intervention through centuries in spite of periodic oak leaf roller outbreaks. And really, as far as people are concerned, these insects are mainly just unsightly and can be a nuisance. They don’t do any real harm.”
Brown said possibly the best “protection” against oak leaf rollers is to wear a cap or broad-brimmed hat and perhaps a long-sleeved shirt outdoors around the house during the weeks when they are most prevalent.
“This may take away some of the ‘ick factor’ of possibly coming in direct contact with them, especially if they are dangling at eye level,” she said.
More information on the oak leaf roller can be found in publication E-206 on the Texas A&M AgriLife Extension Bookstore website, https://www.agrilifebookstore.org/.