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Hylotrupes bajulus (Linnaeus, 1758)

Synonym(s) : 

Common names

  • Capricorne des maisons
  • House longhorn beetle Old house borer
  • Cerambicido de la madera labrada
  • Hausbockkäfer

Classification:

  • Order:  Coleoptera
  • Family:  Blattelidae
  • Genus:  Hylotrupes
  • Species:  bajulus

Frequency index:

5
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Overview

Like most of Cerambycidae, house longhorn beetles are typical xylophagous insects, i.e. they (their larvae) feed on wood.
In Greek language, hylotrupes means “wood-borer”. They naturally and solely develop in dying or dead resiniferous woods, but they are also particularly fond of worked woods (roof timbers, floorings…).
They were in rather scarce numbers in the 19th century, but new building techniques favoured their spreading, especially after the use of industrial roof timbers developed. Along with termites; they are presently public enemy No 1 of resiniferous construction wood in Europe. House longhorn beetles are poor fliers; they mainly creep around.
Among the 250 Cerambycidae species found in France, only 4 species can develop (in our houses, buildings, museums…) at the expense of building timbers and worked woods. Hylotrupes bajulus is the only species that infests resiniferous woods; other species, which belong to the Trichoferus genus, feed on deciduous woods.

Recognition criteria

Adult

Size

Variable, between 10 and 20 mm long and even up to 25 mm ; females are bigger than males.
 

Aspect

Elongate insects, slightly flat dorso-ventrally. Eleven-articled, filiform antennae (longer in males than in females), longer than the thorax but, unlike many other long-horn beetles, much shorter than the rest of the body.
The heart-shaped prothorax has two flat, shiny outgrowths on its dorsal face. Elytra have a rough aspect and have stripes and spots of whitish bristles, more or less visible depending on the conditions in which the individuals died and were kept, and on their colour. The females’ ovipositor is usually quite visible.


Colour

Light brown yellow to very dark brown, more or less shiny.

 

Larva

Size

3 mm when they hatch, an average 20 to 25 mm at the end of their development, and sometimes even 30 mm.

Aspect

Soft, cylindrical body. The head is deep in the prothorax, which is slightly wider that the abdomen. Abdominal segmentation is quite visible. The legs are rather short, but quite visible.


Colour

Shiny creamy to ivory white ; brownish mandibles, thorax brown in its front part and creamy white in its rear part.

 

Development cycle

Males can live up to about two weeks, and females only live one week on an average.
Adults do not feed during their short lives and only ensure species reproduction
Mating is very short (3 minutes) and can occur as soon as adults have emerged. In our climates, adults mate between June and September, and eggs are laid 3 days later at most. About 30 eggs are laid on an average (sometimes up to 200). Eggs are elongate, and bulge out in their middle. They are laid in batches of 4 to 7 in wood cracks, sometimes in old larval galleries when woods are severely infested. They are whitish, and 0.2 mm in length. Incubation lasts between 7 and 20 days.
As soon as they hatch, new-born larvae immediately start threading the wood and bore galleries, always along the grain. Gallery length increases by 1 cm per day.
Larval development lasts between 3 and 5 years and can reach 10 years in unfavourable conditions; its length depends on several factors, in particular on temperature and hygrometry, and on the nutrient quality of the infested woods. When temperature are too low (below 15°C), larvae slow down their activity and await better conditions to resume their development. Nymphosis lasts about two weeks and occurs inside a cavity located near the wood surface. Adults reach the outside world by boring up to 8-mm diameter, oval-shaped exit holes through the wood.
The resulting dust pellets (tiny, cylindrical, 0.8- by 0.5-mm chunks) are mixed with wood debris and very quickly fill up galleries, sometimes very close to the surface but without ever piercing through it. That feature makes the detection of that species’ presence all the harder as the outer surface of the infested wood appears quite sound whereas the inside is utterly eaten up. 

Infected materials

  • Bois d'oeuvre

  • Bois d\’ouvrage

  • Papier

House longhorn beetles are by far the most dangerous xylophagous insects for resiniferous construction wood (beams, joists…)
Very dry wood stored in well heated places particularly attracts those insects; they prefer the soft parts (sapwood), and infest furniture and floorings easily. Outdoors, in addition to dead or dying wood, they develop particularly well in electricity and telephone poles.
Pine wood (maritime pine, Scots pine, Austrian black pine…) is particularly infested; fir-wood, spruce, larch, Douglas pine are thought to be less easily infested.
House longhorn beetles’ mandibles are very powerful: as they move in their galleries, larvae can succeed in piercing through the lead or zinc plaques that cover certain crafted woods.

Geographical distribution

The species is common in nearly the whole of Western Europe, except Ireland. It is also found on the North-American continent, in North and South Africa and in Asia. In France, the temperate climates of our Mediterranean and Atlantic coasts are particularly favourable to its development.

Photos