Question: I found this beautiful bug on my wood pile today. Could you tell me what it is and a little about it? Is it a destructive pest or beneficial?
Answer: It’s interesting that just last week someone brought one of these into the Plant Clinic in a jar. So they must be on the march this time of year!
This is the Banded Ash Borer, Rosalia funebris, and a member of the Cerambycidae beetle family. This longhorned wood-boring beetle is a native species in Oregon, and can be found from Alaska to southern California and in the Rockies from Idaho to New Mexico.
Longhorned beetles are typically very large with long antennae. In the case of the Banded Ash Borer, their antennae are much longer than their body and decorated with striking black and white bands. Their body, which can be 1-1 1/2 inches long, also displays the black and white banding, and its white thorax has a distinguishing large black spot in the center.
The larvae of the Banded Ash Borer bore tunnels in the trunks of dead maples, ash, oak, alder, willow, sycamore and Oregon myrtle. Since they bore into dead wood, these insects are not considered harmful or destructive. In fact, they are beneficial as they remove and recycle old and sick trees. The larvae may also be a food source for woodpeckers and bears.
The females lay their eggs individually on small- to medium-sized dead branches. Hatching within seven to 14 days, the emerging larvae feed for six to seven months under the bark, creating tunnels that are round or oval and filled with fibrous, coarsely granular or powdery frass (feces).
These larvae then overwinter as pupae in the center of the branch. When spring comes around, the pupae emerge as adults, chewing their way out of the branch.
The adult beetles are usually found singly from March until August. But if you have a freshly-painted house, as was the case with our Plant Clinic visitors, you may find more of them congregated about because the paint gives off an odor that closely resembles their mating pheromones.
These beetles are sometimes mistaken for the invasive and destructive Asian Longhorned Beetle (Anoplorophera glabripennis) as well as the Citrus Longhorned Beetle (Anoplorophera chinensis), which are posing a serious threat to Pacific Northwest forests and landscapes.
These exotics from southeastern Asia are similar in appearance with mostly shiny black bodies that are spotted with small white dots, not bands, and their thorax behind the head does not have the tell-tale large black dot of the Banded Ash Borer.
The Asian Longhorned Beetles are seen in the eastern states, but the Citrus Longhorned Beetle has been found emerging from shipping pallets in Bellingham, Washington. So if you happen to see either of these exotic beetles, please report them to our Plant Clinic.