Roundheaded Borers and Longhorned Beetles

Description of roundheaded borers and longhorned beetles

One of the families of beetles with the largest number of species is the Cerambycidae. The adult beetles in this group are called longhorned beetles because of their long antennae. The immature stage of most longhorned beetles is a woodboring larva called a roundheaded borer.

There are hundreds of species of longhorned beetles and many are very common. The beetles vary in size from 1/4 to 3 inches long. The longhorned beetles are attracted to dying, freshly cut or recently-killed trees where they lay eggs on the bark of the green wood. The larvae emerge from the eggs and burrow into the tree and spend one to three years tunnelling through the wood. Tunnels may be just under the bark or in the heartwood, are usually about the size of a lead pencil, and are packed with coarse sawdust. The larvae are wormlike and white to yellowish with a brown head, round-bodied and deeply wrinkled. Holes and piles of sawdust mark where the adult beetles emerge from the infested wood.

Damage caused by roundheaded borers and longhorned beetles 

Roundheaded borers are commonly found in firewood, and the longhorned beetles may emerge from wood brought into the house. These beetles may also wander into houses by mistake as "accidental invaders." Longhorned beetles crawl about the house creating a nuisance but they cannot bite, sting, attack furniture or damage the house structure. They do not infest cured lumber (such as in the house structure or in furniture) nor dried firewood.

Management of roundheaded borers and longhorned beetles 

The best way to prevent the nuisance of insects emerging from firewood is to leave the firewood outside until it is to be burned, bringing at most, a few day's supply into the house at one time. Beetles that do emerge from firewood inside the house need only be picked up and thrown away.

Spraying firewood with an insecticide is of very little benefit and potentially dangerous. Therefore, we strongly advise against treating firewood. Insecticides will not penetrate deeply enough into firewood to control roundheaded borers or emerging longhorned beetles. Storing and burning insecticide-treated firewood indoors could be a health hazard as the insecticide is vaporized into the living area of the house.

Do you live in Iowa and have an insect you would like identified?

The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them.  Please see our website for current forms, fees, and instructions on preserving and mailing insects.   

Contact information for each states diagnostic laboratory for U.S. residents.  If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.  

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 13, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.