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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Beetles roasting on an open fire: Roundheaded borers, Cerambycidae, and Darkling beetles (Family Tenebrionidae)


Red milkweed beetles adorn milkweed florets in summer. 


With the return of chilly winter weather, it’s time to split a few logs for the fireplace. As you wield your maul, take a few moments to peel back the loose bark on the logs. You might be surprised by what you find.

Galleries like these beneath the bark of my firewood are often made by roundheaded borers. 

If your firewood is not too old and rotten, just beneath the bark you may find serpentine galleries that wend their way along the surface of the hard wood. Examine the inner surface of the bark and you will see the mirror image of this trail. Galleries like these are often created by larvae called roundheaded borers and my maple logs were chock full of these borers. After completing development beneath the bark, they chew a round hole to the outside of the log and emerge as a longhorned beetle, so named for the remarkable length of their antennae. Many species of roundheaded borers like the ones tunneling through my maple logs prefer to eat the tissues of dying or dead trees. 

Roundheaded borers have powerful jaws but usually lack legs.


Some, like the dreaded Asian Longhorned Beetle, attack living trees. Since its introduction into the United States in the 1990’s, this beetle is responsible for the death of thousands of landscape trees in New York, Chicago, New Jersey, and, more recently, Massachusetts. Roundheaded borers that eat wood have powerful jaws to chew their way through the hard plant tissues. The adult longhorned beetles can be found on flower heads, where they eat nectar and pollen.

The adult stage of a roundheaded borer is a longhorned beetle, named for its very long antennae. 



While adults of the magnificent red milkweed beetle feed on flowers, its larvae eat the roots of the milkweed. Longhorned beetles are also attracted to porch lights in the warm months of the year. If you bring firewood into your home and store it for an extended time before you use it, you may be treated to the emergence of several wonderful longhorned beetles.




A gang of darkling beetles find winter refuge beneath bark.


As I peeled back the lose bark of a second log, I discovered a bevy of darkling beetles. Darkling beetles spend the winter in a frigid scrum beneath the bark of trees awaiting the warmth of spring to resume their activities. Most darkling beetles feed on plant material of some sort, living or decaying. The larvae of some species of the darkling clan go by another common name, mealworms.

Although he is moving rather slowly now, this darkling beetle larva will develop quickly when warmer temperatures return,



Mealworms occasionally become pests of stored products, such as grains and cereals, in the pantry. They are also prized bait of fishermen. Not far from where the adult darkling beetles huddled, several darkling beetle larvae moved at a glacial pace through the decaying wood beneath the bark. Like their roomies, the roundheaded borers, darkling beetle larvae will complete their development when the warmth of spring returns. So, on a wintry night “while you are singing the songs you love to sing without a single stop at the fireplace while you watch the chestnuts pop, pop, pop”, listen carefully….there may be more than just chestnuts popping.



For more information on roundheaded borers and other borers in firewood, and darkling beetles, please visit the following web sites: