April, 2006

Red-Headed Ash Borer

Some of our most spectacular beetles belong to the family Cerambycidae, or long-horned beetles. The red-headed ash borer (Neoclytus acuminatus) is not large, measuring only about 1/2 inch in length, but it is an arresting insect in both color and habit. The beetle's head is actually rather small and the bulbous bulk of the "red" part is the next body segment, called the pronotum. This particular borer lays its eggs on the bark of dead logs from ash trees and the resulting larvae eat the inner wood. The long antennae of the adult are quite characteristic of this family, hence the name long-horned.

We don't often have the specific species of dead wood that attract this beetle just lying about in our yard, but we sometimes prune our ash trees and leave the branches piled in the compost bins until we can saw them up for disposal. This is enough to lure in these borers. When I first saw one, I thought it was a wasp, as the movements and general coloration were extremely similar. Most beetles are reluctant to fly, as they must unfold their inner wings from under the hard outer ones. Once they do get airborne, they are usually awkward. The red-headed ash borer, however, is a fast and agile flyer, making the wasp mimicry quite convincing. Once the insect lands, it darts about with short, fast motions, much like a real wasp. Only when the beetle pauses is it easy to see its actual identity.

When the preferred wood is available in our yard, there are often several beetles in the vicinity, and they can then be seen searching around and mating.