Red Oak Borer

When we think of invasive or damaging insects we generally consider it to be some non-native culprit yet again wrecking havoc in a Country it does not belong, namely ours. Face it, it happens all too often, just consider this, none of the following insects are native to the US, but have caused untold amounts of damage from their feeding habits.
1.) Japanese Beetles
2.) Asian Longhorn Beetles
3.) Multi-Colored Asian Lady Beetles
4.) Emerald Ash Borer

All of these species cause damage, each in their own way and nearly all were accidentally brought to our Country. Some showed up in shipments of plants from Asia, and others were purposely brought here to control native species that "scientific specialists" felt needed a more specialized predator to control, since in their opinion our own were not doing a good enough job....i.e. the Multi-Colored Asian Lady Beetle. This ladybug-like beetle was brought here to control aphids in forests, several attempts to release it into the wild beginning around 1916 were not successful. Eventually populations of them showed up in shipments of plants in a greenhouse in PA and some escaped. For whatever reason conditions were perfect and they were able to establish themselves and spread westward. The rest is, as we would say, history.

Sometimes for unknown reasons a native species becomes a problem, and such is the case with the Red Oak Borer (Enaphalodes rufulus). The ROB is native to the Eastern United States and parts of Texas and feed on oak trees, especially red oaks (Although they will sometimes jump ship, so to speak, and feed on maple and hickory trees).  Up until about 2005 they were a minor pest in oak timbers, but something flipped the switch with these longhorn beetles, their numbers increased significantly, and suddenly they were wrecking havoc on oak forests throughout Southern Missouri, and Northern Arkansas as well as other areas throughout their range.

Red Oak Borers are fairly large beetles in the longhorn family that may reach lengths up to 28 mm (1 1/4 inches). The males have antennae twice as long as their body, females have shorter antennae that are about the same length as their bodies. Overall they are reddish-brown and covered in golden scales, called Setae. These scales are often rubbed off leaving patches of reddish-brown showing. This gives them a mottled appearance. This coloration gives them perfect camouflage which allows them to blend into the bark of the trees they favor. It is easy to pass them by without ever seeing them.

Males use their long antennae to smell the pheromones (Chemical perfume) that the female exudes to attract him. After mating, the female will begin to lay eggs about 8 to 10 days later. She will deposit approximately 100 eggs in her lifetime and each one is placed in the bark crevices of oak trees. When the eggs hatch the tiny grubs will burrow into the tissue behind the bark of the tree and remain there for about a year feeding. During the second year of their development they are much larger and will burrow into the heartwood of the tree. This is when the beetles become a problem to the timber industry. Their feeding habits create long tunnels throughout the valuable timber.


After two years their lifecycle is complete and they will begin emerging sometime in May (or June) depending upon where they live. Their emergence typically takes place at night and they are often found at porch lights or other light sources. While they do have a lot of natural predators, including woodpeckers, that use their long beak to locate them under the bark of trees, also sap beetles, ants and carpenter worm larvae all enjoy a tasty red oak borer grub for a meal. Even though many thousands of grubs are killed this way, and estimates are that 15% will survive to adulthood, it doesn't seem to affect their numbers in any real significant way.

Adult beetles exit the tree via a 1/2 inch hole they have bored into the tree to the outside world.  It may take 2 years for wounds left by these beetles to heal, and fortunately death of the trees is rare unless the tree is already weakened or damaged in same way and cannot withstand an onslaught of feeding grubs.

The feeding habits of the grubs cause significant damage to the timber, which is used for lumber. The defects caused by their tunneling makes the wood worthless to markets that would typically demand the highest prices for quality oak boards. This has resulted in millions of dollars in losses to the oak timber industry. It is also not entirely uncommon to have lumber shipped overseas and have beetles emerge from the boards, which creates an invasive species situation in those countries.

I've not been able to locate any information as to why this beetles numbers have increased so exponentially over the past decade or more. Could it be fewer predators feeding on them? Is it an increase in food sources? Is it the irresponsible moving of timber from one area to another, either in the form of firewood, or logs meant for lumber? By whatever means their numbers have increased, it is obvious they are here to stay and will continue their feeding frenzy on oak trees.