Anobiidae belong to the order of xylophagous (wood-eating) beetles, which means that the larvae of some species attack wood. There are two species found mainly in dwellings: Anobium punctatum or anobium beetle or common furniture beetle, and Xestobium rufovillosum or death watch beetle. They are known for the damage they cause in antique furniture, and many people wrongly believe that their presence is a sign of authenticity for this type of furniture. This insect is also, if not more frequently, found in floor and structural framing.
The adults of the furniture beetle (2.5 to 5 mm) and the death watch beetle (5 to 7 mm) have massive and globular bodies, and their heads are hidden under the hood-shaped thorax. The furniture beetle has an elongated shape and is chocolate brown in colour, with spots on its elytrons, while the death watch beetle is stockier and dark brown, with a marbled appearance caused by tuffs of yellowish hairs. The larvae (5 to 7 mm for the furniture beetle and as much as 11 mm for the death watch beetle) are humpbacked, creamy white in colour, and covered with hairs. Their thorax carries three pair of feet.
|Death watch beetle
Biology and behaviour
Their eggs – 25 on average for the furniture beetle and 50 on average for the death watch beetle – are generally laid in summer, in cracks in wood. They are milky white and barely 0.5 mm in length. The larvae hatch four to five weeks after their eggs are laid. As soon as they emerge, the larvae dig galleries in the wood, and the process continues throughout its development, which varies according to the temperature, humidity, and nutritional value of the wood. The furniture beetle larval stage spans two to four years; that of the death watch beetle, three to five. The larval stage can continue for up to 10 years if environmental conditions are unfavourable.
When the larvae are ready to change into pupa form, they dig a chamber very close to the surface of the wood and live in it two to three weeks. The adults emerge in this chamber and dig an exit hole in the wood. After emergence, the adults mate and the females take off in search of wood to lay their eggs. Their life is dedicated solely to reproduction. Adults do not eat; they live between three and four weeks, in the case of the furniture beetle, and eight and ten weeks in the case of the death watch beetle. It is not unusual to find females laying their eggs in old exit holes; if the environmental conditions there were favourable for their progeny, it makes sense to return to the same spot. It should be noted that the wood damage is caused mainly by the larvae.
Places they can be found in the home
Beetles live naturally in the outdoors, but they get along very well in dwellings. They attack lumber and timber in particular (framing members and floors), but also furniture, works of art and libraries. The furniture beetle shows a preference for green wood and develops equally well in both deciduous and conifer species. Death watch beetles can also develop in deciduous and conifer wood, but unlike the furniture beetle, green wood is essential to their development. The moisture causes xylophilous fungi to grow in the wood, and the nitrogen produced by the fungi and the water provide the nutrients the beetles need to develop. A minimum of 22% moisture content is vital to fungi development and, consequently, to larvae development. The temperature should be between 20 and 25°C. Beetles appear to spare tropical species.
Beetles are attracted by green wood, so excess moisture should be eliminated from problematic rooms. The moisture is often linked to water infiltrating from the roof, pipeline, cracks, or water damage from storms, floods, etc. To prevent infestations you should check the condition of the wood on a regular basis, look for the appearance of indications of their presence (exit holes, feces, presence of adults near windows), do away with any sources of moisture conducive to xylophilous fungi, and take care in choosing the quality of lumber to use for construction. Preventive physiochemical treatments can be applied.
Signs of infestation
The adults of the furniture and death watch beetles make typically circular exit holes in the wood. The furniture beetles’ holes measure 1 to 3 mm, and the death watch beetles’, 2 to 4 mm. The holes are more or less localized and numerous. Generally speaking, only the parts rich in sapwood (cambium layer) are attacked, but such attacks can extend to the heartwood if it is not duramenized (e.g., pine). In the case of fungal development, the duramen of resistant species can be attacked. Piles of wormhole dust may appear on the surface of infested wood. Since the larvae do not dig galleries outside the wood, the damage can be considerable before the adults’ exit holes become apparent, especially since it may take several years for the holes to appear, as mentioned above. Surveys have determined that the number of first-generation insects increase by a factor of 10 in 10 years. Their presence in dwellings means that unprotected solid wood furniture will be contaminated over the more-or-less long term.
Adults also have the ability to fly and are attracted by daylight. They can therefore be found walking along windows sills or near the windows. If adults are detected in dwellings, you should find out where they came from by looking for exit holes.
The beetles’ presence can also be confirmed by observing their characteristic feces (using a loupe or magnifying glass). The furniture beetle’s excrements are very tiny, cylindrical and long, while those of the death watch beetle are rounder, thicker and resemble tiny lentils. Since both beetles may cohabitate, the presence of one does not rule out the presence of the other.
With beetles, prevention is the best control method. If an infestation does occur, in spite of the methods employed, the first thing to do is determine the extent of the damage. If it is a light infestation in a piece of wooden furniture or accessory, the best thing to do is have the item stripped and a residual insecticide applied. For larger infestations, the item should be fumigated in a room specially provided for the purpose. It should be noted that most of the furniture imported into the country has been fumigated using this technique.
When framing members or floors have been subject to serious attack, the wood must be replaced; otherwise, the house could end up as a pile of dust. Better ventilation is also recommended. For moderate or light infestations, yearly application of an insecticide, over a period of at least three years, is advisable (to cover the insect’s life cycle).
Other interesting facts
The death watch beetle is also known as the knock beetle or death clock beetle because a sharp, rhythmic and periodic sound is often heard in the silence of the night in wood infected by this insect. The sound is made by adult females rapping their foreheads against the wood to attract males (a nuptial display). People used to believe that the noise was announcing the death of someone.
Beetles are good actors since they are able to “play dead”. Given the fact that they are able to remain motionless for long periods of time, you should not take it for granted that they are dead.