Latin: Hylotrupes bajulus
Hylotrupes bajulus is the Latin name for the house longhorn beetle, which belongs to one of the wood pests that can most quickly cause great damage to timber. Also, in Denmark, the house longhorn beetle rises several problems when it settles in roof constructions and other timber.
Appearance
The house longhorn beetle is a beetle that can grow 10-20 millimeters long. The beetle comes in several color variations that change from the light brown to the completely black.
One of the most characteristic features of the house longhorn beetle is its woolly, whitish hair on both the back and fore chest, which forms two oblique whitish spots. On the chest it also has two shiny knots. The house longhorn beetle’s wings, which are located under the coverts, are large and clear. The house longhorn beetle has two antennas that are divided into 11 joints.
The house longhorn beetle larva is almost milky white, but also has some dark chitin parts placed around its mouth. The larva is equipped with small legs that are barely visible to the naked eye. It can be up to 25 mm long.
Biology and behavior
The house longhorn beetle belongs to the family wooden bucks (Cerambycidae). It is rare to see the adult house longhorn beetle as they mostly stay in their hiding place in the tree. In the middle of summer, however, the beetles emerge to mate. But after mating, the female secretly seeks a suitable place – preferably in a crack in a dry coniferous tree. The female finds its way to the coniferous tree with the help of the special fragrances found in the resin that penetrates out of the deep dry cracks in the tree. Sometimes the female also chooses other types of cracks than those found in the wood, such as boards and other woodwork as well as joints in furniture that consists of softwood.
The female lays her eggs in the cracks using her long laying tube, which – when she rests – stick out behind her coverts like a small pin. The female places her eggs about 20 millimeters inside the cracks in portions of 20 to 30 eggs. A house longhorn beetle female lays eggs for a few weeks, and during this period she can manage to lay several hundred eggs. The adult house longhorn beetle only lives for 10-15 days.
After the larvae have hatched from the eggs, they gnaw into the tree through a small hole. Their journey goes towards the outermost layer, which is the most nutritious. The larvae eat the layer without at the same time gnawing through the surface of the wood. After this, the larvae gnaw further inwards, but no further than to the very core of the pine tree, which they cannot digest.
There are many factors that come into play in relation to the larval development process. Under normal circumstances, the development from egg to adult beetle will last between two to five years, but it is also not without precedent that the development can last as long as 10 years. Here, temperature plays an important role first and foremost. In the Danish climate, development can therefore go faster if the house longhorn beetle settles under black slate roofs than under a red tile roof.
As the house longhorn beetle larva eats its way through the tree, it also leaves a trail of its own excrement behind. These excrements are small roller-shaped particles which, together with the gnawed wood chips, are transformed into the so-called drilling dust. The drilling dust is pressed tightly together in the passages, so that it eventually forms a solid mass. Often, the presence of the drilling dust alone will be an indicator that a house longhorn beetle is at stake in the woodwork. But also, the house longhorn beetle’s relatives leave similar traces. For instance, the viola buck, which always has remnants of bark in its drilling dust.
The house longhorn beetle larvae gnaw its way to the surface of the tree, just before it turns into a beetle. Once it has reached a certain size, it is even possible to hear its gnawing sounds. Below the surface of the tree, it arranges a small pupa in an extended area at a time. Here, the transformation takes place from first pupa and then adult house longhorn beetle. When the development is complete, it breaks out of the surface of the tree through its flight hole. Preferably on a hot summer day.
Together with the drill dust, the fly hole is a clear sign of the house longhorn beetle’s presence. The flight holes are most often oval and often have slightly frayed or irregular edges. The holes are predominantly between 6 and 10 millimeters long.
Damage
Dry coniferous wood is most often the hearth for the house longhorn beetle’s excesses. Unfortunately, this is also the type of wood materials most often used for roof constructions. During the summer months, it is not uncommon for the temperature of ceilings to be high enough for the house longhorn beetle to have the best conditions for reproduction. Therefore, woodwork and timber in the attic are at particular risk of being exposed to the attack of the beetle.
The chance of finding an active house longhorn beetle attack is under the influence of the age of the house. If the house is less than five years old, it is rarely possible to find any attacks. But the risk increases until the house’s twentieth year, after which it will fall again. If the house is more than 70 years old, it is one of the rarities that a new attack is underway. Unless the house has had new woodwork installed in connection with repairs.
Prevention and pest control
The control of the house longhorn beetle can be a difficult undertaking, as it is the larvae that make up the largest part of the population. And since they are inside the woodwork, they can be hard to come by to fight. However, it is recommended to use heat that can penetrate the wood or use a liquid wood preservative to control house longhorn beetle. A surface treatment can also be a solution, but it requires removing the most infested layers and brushing the surfaces clean. Be sure to treat cracks and crevices thoroughly. The treatment can be supplemented with post-impregnation, such as borehole irrigation or pressure injection, if the timber is partially unavailable. As a preventive measure, wood that has been surface-treated should be used in the future.
"Pests in House and Home"
"Bed Bugs - Bites, Stings and Itches"
"Food Pests"
"Husets dyreliv" (Insects Around the House - Only danish)
"Skadedyr i træ" (Timber Pests - Only danish)
"Stuefluen" (Common Housefly - Only danish)