Hosts:  Douglas-fir, pine and true fir

Figure 170. Boring at base of ponderosa pine caused by carpenter ants

Symptoms/Signs:  Carpenter ants are large in size, about 5-15 mm long, and black or black and red in color. They tunnel in the wood of stumps, logs, dead standing trees, the interior dead sections of livings trees, and the wooden portions of buildings. These galleries are honeycomb-like in appearance; the walls are sandpaper smooth, free of frass, and run across the grain. The wood borings, which are coarse and fibrous, are pushed out of the tunnels and may accumulate at the base of inhabited trees.

Biology:  Mating occurs during mass flights in the spring. The female then lays eggs, which take approximately 2 months to become mature larvae. The larvae then pupate in cells. Each individual will emerge as one of three possible castes: winged males, winged females, or workers. Carpenter ants do not eat wood but excavate galleries for nesting purposes. These insects are general feeders, and will eat animal food (such as caterpillars, meat, or refuse) and sweets (from aphid honeydew, ripe fruit, or sap.)

Effects:  The excavations in wood can be so extensive that the structural integrity of the tree is lost, predisposing the tree to wind breakage.

Figure 171. Cross section of stump with carpenter ant galleries.

Similar Insects and Diseases:  Horntails or “woodwasps” (Siricidae) have similar excavations in host trees. The main differences being that they actually have the wood borings pass through the digestive tract and are packed in the tunnel behind the larva. They usually attack fresh logs or newly dead trees. Adults are generally thick-waist, wasp-like insects that are metallic blue or black in color. Adults emerge in late spring or summer and lay eggs in solid wood (conifers or hardwoods) and the life cycle can range from 1 to 2 years. Pupal cells are found in the phloem and the exit holes from mature adults are round.

References:  15, 24