HPIPM:Ponderous Borer

From Bugwoodwiki

Compiled by Whitney Cranshaw, Colorado State University:

Colorado Insects of Interest

Ponderous Borer

Figure 1. Ponderous borer male (left) and female (right).

Order: Coleoptera (Beetles)
Family: Cerambycidae (Longhorned Beetles)

Identification and Descriptive Features: The ponderous borer is an extremely large beetle, ranging from 45-60 mm length, with an elongated body form. It is generally dark brown but may have lighter brown areas of the wing covers. The larva is a very large roundheaded borer that is overall creamy white except for the dark mandibles associated with the head area

Distribution in Colorado: The ponderous borer develops in the roots of various pines and has a likely distribution within Colorado that largely overlaps that of ponderosa pine. Museum records from the state include Larimer, Boulder, Jefferson, Elbert, Chaffee, Fremont and Pueblo counties east of the Continental Divide and LaPlata and Archuleta counties in southwestern Colorado.

Life History and Habits: Adults are present from early June through August. Females lay eggs in the bark crevices of dead pine trees and stumps. The larvae subsequently excavate large tunnels through the sapwood and heartwood over the course of several years. Pine logs are most commonly used by this species.

The ponderous borer only develops on fallen or recently killed trees and is not a threat to live trees. However, this is the largest beetle found in Colorado and their large size commonly attracts attention and concern. Larvae of the ponderous borer are sometimes known to foresters as “timber worms”.

Species of Similar Appearance: Some longhorned beetles in the genus Prionus that occur in Colorado also reach very large size. These tend to be a bit darker colored and have a slightly blunter body form. Antennae of the Prionus spp. also are more enlarged than on the ponderous borer, particularly among the males. Prionus longhorned beetles develop as root borers of grasses, shrubs and some trees.

Figure 2. Female ponderous borer visiting a lightning struck tree for egg laying. Photograph by David Leatherman.

Figure 3. Ponderous borer larva, aka a “timber worm”. Photograph by David Leatherman.

Figure 4. The California prionus (Prionus californicus) is another large longhorned beetle that is present in Colorado. Larvae develop as root borers of various deciduous trees and shrubs.

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