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Common Name: Flat Bark Beetle
Scientific Name: Cucujus clavipes

(Information for this species page was gathered in part by Ms. Veta Obazenu for Biology 220W at Penn State New Kensington in Spring 2011)

Flat Bark Beetle - image credit B. Smith, FlickrThe flat bark beetle (Cucujus clavipes) is a member of the superfamily of beetles called “Cucujoides”. Cucujoides contains 36 families of beetles and many thousands of species that range from the predaceous “ladybug” (or “ladybird”) beetles, to numerous species of fungus beetles, to a wide range of “bark beetles.”

The flat bark beetle is found in forested habitats of northern North America (Alaska, Canada, and many northern and central U.S. states). Adults are around one half an inch in length with dorsoventrally flattened bodies that are bright red in color. Their antennae and several leg segments are black, and they have large, triangularly shaped heads. Their bodies are quite smooth and free of any hairs. The body shape and surface design enables this beetle to move about easily in the tiny crevices under the bark of its host trees.

Image credit: B. Smith, Flickr

Adults are typically found under the bark in living or freshly cut trees although they might also be present in old logs and even in the leaf litter around fallen or cut trees. Tree species that seem to be preferred by the flat bark beetle include poplars, ashes, and oaks, but they are also found in a wide range of other species of trees. The adult flat bark beetles are active predators within their constricted, sub-bark micro-habitat.

Larvae of the flat bark beetle are slightly larger than adults (around one inch long). They are usually amber in color with forward protruding mouthparts with mandibles and apical teeth. The structure of these larval mouthparts seems to infer that the larvae, like the adults, are also predators of a wide variety of mites and insects (especially insect larvae) that are found in the spaces and galleries beneath the bark of their host tree species. The larvae do not have eyes and, so, must be able to find their prey by either tactile or chemical sensory systems. Because the flat bark beetle preys on this vast array of potentially tree damaging invertebrates (especially the larvae of the “true” bark beetles that spread fungal diseases among a wide variety of tree species), they are considered to be beneficial to the survival and health of the living trees.


Reproduction and Mating
Adults mate in the spring. Mating pairs find each other via pheromone cues. Eggs are laid under the bark typically of living trees. Eggs hatch into larvae which will then spend the next two years feeding and growing under the bark of their host tree. The larva will eventually pupate. Pupae persist for two weeks, and then adults emerge in the late summer or early autumn.

Both larvae and adults are able to tolerate extremely cold, winter temperatures without significant damage to their cells or tissues. This cold tolerance is due to the buildup of glycerol and antifreeze proteins in the intracellular and extracellular fluids of the beetle. These beetles can retain a very high percentage of body water throughout the winter because of the efficiency of these antifreeze chemicals.

Predators of the flat bark beetle are poorly described. Other, larger predaceous beetles would presumably prey on both larvae and adults, and it is expected that woodpeckers would be able to open up probing holes in the tree bark to find and extract especially the flat bark beetle larvae. The susceptibility of flat bark beetle larvae and adults to fungal and bacterial diseases is also not well known.

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