Latin: Callidium violaceum
The violet tanbark beetle is a pest that belongs to the cerambycidae family. It is characterized by its large size.
Appearance
The adult violet tanbark beetle is easy to recognize due to its beautiful violet blue color. In contrast, the larvae are difficult to distinguish from each other, as they appear as pale, chubby, or flat larvae. In the front, the larvae are wider with a strong and dark cheekbone.
An adult violet tanbark beetle is equipped with laying tubes at the rear end which is used to lay and place eggs in cracks and crevices.
Biology and behavior
This insect only lays its eggs in conifer, dead or demolished trees, still bark clad.
The larvae live in the layer between the bark and the sap wood, and they always move beneath the surface. The larvae move in passages, those will be seen as channels in the sap wood. These passages are traces from the larvae cheekbones. Likewise, it will be possible to find drilling dust from the larvae in those passages which is actually their excrements. The drilling dust is easy to recognize from that of a longhorn beetles, as the excrement from the longhorn beetles is yellowish.
The development from larva to adult violet tanbark beetle takes in average 1-2 years. When the larva is fully developed, it will gnaw a 3-5 cm long passage into the wood, thereafter it will pupate in an enlarged den. It will close the den with rough wood dust. When fully developed, the violet tanbark beetle will emerge through the same hole as the larva entered and chew an oval exit hole of 6x4mm.
You can encounter this species in June and August, but in conifer firewood, you can lure them out by heat all year round. Besides new generations may occur from this pest until the entire bark layer of the conifer is used.
Damage
Wood boring beetles is a pest that many fears. The violet tanbark beetle should however not be feared, as it is the house longhorn beetle that is a serious pest. The violet tanbark beetle is normally completely harmless, but they do attack the tree barks, however those attacks do not spread to debarked wood. The damage from the violet tanbark beetle, has no effect on the load-bearing capacity of the wood but it will have a practical meaning to the wooden boards that is clad with bark. Here the pest can gnaw its way out through the plates.
The damage will be severe on wood boards, if lead or cardboard roofs has been laid directly on top of the bark-clad wood. The holes from the pest can result in water damage as well as an increased risk of fungus or rot.
Prevention and pest control
If you want to avoid an attack from violet tanbark beetle in conifers, you should use debarked planks. It is rarely necessary to control this pest, as the attack will die out by itself, when the layer between the bark and wood is eaten.
If you want to avoid violet tanbark beetle, it will be best to remove all bark residues. If you do have boards directly applied to bark-clad wood, it will be difficult to prevent a potential attack. Here you will cause more damage than what the violets can cause. Instead, it is often sufficient to repair the flight holes as they occur, as the attack will die out by itself.
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