Common Oak Moth

The common oak moth (Phoberia atomaris) showed up in Ross County in 2002. This insect, despite its name, is not all that common in Ohio.

However, in keeping with its name, the caterpillars were feeding on oak. The common oak moth can be found from Massachusetts to Florida, and west to Kansas and Texas.

Common Oak Moth

The common oak moth (Phoberia atomaris) showed up in Ross County in 2002. This insect, despite its name, is not all that common in Ohio. However, in keeping with its name, the caterpillars were feeding on oak. The common oak moth can be found from Massachusetts to Florida, and west to Kansas and Texas.

The caterpillars are nearly an inch long, thick bodied and hairless. They have black markings, especially paired black triangles down the back, and irregular brown lines down the sides. While some older literature indicates that there have been major outbreaks of this caterpillar in the past, I have never seen them in Ohio. Neither had my Ohio colleagues at Ohio State University Extension…and they’ve seen just about everything!

There are historical records of the insect in Ohio, most recently in the late 1990’s. In the Missouri Ozarks, a common oak moth outbreak severely defoliated post oaks in 2001. Their numbers were much lower in that location this year.

The outbreak this year in Ohio seemed to be confined to Ross County. There were a few caterpillars reported in Athens County. The most heavily damaged area was at Scioto Trail State Forest, where the Division’s aerial survey detected 8,600 acres of severely defoliated oaks in June.

While the literature states that all oaks are suitable hosts, white oaks seemed to be favored in this outbreak. In many cases, the white oaks were completely defoliated, resulting in subsequent re-foliation. Many trees were in poor condition and have already died, other trees will decline or recover depending on environmental conditions during the next few growing seasons.

Did the common oak moth kill the trees? They certainly contributed, but the trees were already stressed and larvae of the two-lined chestnut borer (known to attack declining trees) could be readily found under the bark of the trees.

It is also important to remember that in 1999 a drought affected this area of the state. In addition, tent caterpillars defoliated trees in Southern Ohio, including white oaks at Scioto Trail Forest, in 2000 and 2001. Then another drought affected the area in 2002, immediately after the common oak moth defoliation.

Clearly, the white oak trees that died at Scioto Trail State Forest this year succumbed to a series of stress events over a 4 year period, with a secondary insect (two-lined chestnut borer) finishing them off at the end.

Pesticide treatment was not recommended in 2002 because the common oak moth has only one generation per year and its population is likely to collapse before next year from natural factors. We’ll be watching what happens next spring. If necessary, shade and ornamental trees can be protected with any insecticide labeled for caterpillars.

If you have questions about a forest pest call your local forester.