Common furniture beetle and woodworm

common furniture beetle

The Common Furniture Beetle (Anobium Punctatum) woodworm belongs to the family Anobiidae which contains at least twenty-two different species in Britain and includes the Death-Watch Beetle and Biscuit Beetle (Stegobium Paniceum). The “common” name with its emphasis on ‘furniture’ is inappropriate as it is most often found in structural and joinery timbers in buildings.  It tends to be called, woodworm as it’s the larvae of the common furniture beetle which bores into softwood and sapwood and pupates into a beetle and at this point it leaves the timber, which we call on exit holes of flight holes and the circle of life starts again.  The common furniture beetle’s woodworm is the most prevalent wood-bora in Britain’s homes and feeds on the building’s timber.

Its Life Cycle

Mating: –This takes place often within a few hours of emergence from its exit hole as a beetle. The fe­males will sometimes stay in old exit holes, both before and after mating,  the act of mating can take place with the female just inside an old flight hole with the tip of her abdomen just protruding and the male on the outside.

common furniture beetles' egg

Eggs: –The female lays her eggs in cracks of unpolished or unpainted wood or sometimes in old exit holes.  The eggs are laid in groups, but not necessarily all being laid in the same place, as there may be 20-100. The eggs are oval in shape but pushed out of shape when forced into timber crevices during laying. The young larvae emerge after about three to five weeks from the base of the egg and boring into the timber.  The eggs maybe visible, but the larval entrance holes are not. It is important that the egg be firmly attached to the wood for the newly hatched larva to successfully penetrate the timber.  If eggs are disturbed it is unlikely that re-infestation will occur.

common furniture beetle larva

Larva: – The larva is whitish in colour and is covered with fine hairs.  Its head is yellowish brown with dark brown jaws and has a hooked or crescent shaped and remains within the wood, tunnelling up and down the grain and occasionally across the grain to access a new sapwood growth ring.  Its tunnels are circular in cross-section, each up to 2mm in diameter.  This work takes place throughout the year and the tunnel section behind the larva is loosely filled with bore dust/ frass which consists of chewed wood and fecal pellets. These pellets are variously described as ellipsoidal and lemon shaped which gives the bore dust a ‘gritty’ feel.  A fully grown larva can be 6mm long with three thoracic segments each bearing a pair of five jointed legs and will have cast its skin several times.  During the spring of the year in which it matures it will burrow towards the surface of the timber and form a slightly enlarged chamber which is free from bore-dust and just below the timber surface.  In the chamber it changes from a larva to a pupa.

Pupa:-  At this stage of the cycle which lasts from two to eight weeks then metamorphosis takes place and the body tissues become reorganized so that a creamy-white adult shape can be recognised with legs, wing-cases, antenna etc., held in a thin transparent pupal skin. It can move only the last few segments of the abdomen but at maturity the pupal skin bursts off and an adult beetle is born. It spends a period of rest whilst the skin parts harden and turn brown then bites its way out into the open air through what becomes known as the exit hole, emergence hole or flight hole.  The merging beetle often has to contend with paint and varnish and other surface coverings, and some beetles are strong enuf to bite through lead flashings.  The emergence on the beetle usually takes place between May and August, chiefly in June and July although random emergences.

common furniture beetle

Adult: – The adult common furniture beetle varies from 3-5mm in length (the larger ones are often female) and are reddish brown to dark brown colour. The prothorax or chest is hood shaped and when viewed from above almost completely hides the head.  A 180-degree angle exists between the hood and the edge of the wing covers and to a greater or lesser extent hooding of the head is shown by all members of the Anobiidae family.  The two front wings have been modified as wing cases or ‘elytra’ which have longitudinal rows ‘punctures’ or small pits. The upper parts of the body are clothed with fine short yellow hairs.  Its adult beetle stage extends over two or three weeks only, during which time it does not feed so the only damage it does is in forming the exit hole.  The length of the common furniture beetle’s life cycle depends on the species of timber and its condition also temperature and moisture level.  Indoors it can survive around three years although five years is not uncommon.

Damage to timber

woodworm damage to floor

The extent of damage to the timber is governed by the species of timber, whether it is fast or slow grown, and most importantly the sapwood content.  It is rare for a woodworm infestation to cause structural failure.  But it may occur with a concentrated infestation, especially when the timber is fast grown with a very high sapwood content.

The moisture content of the timber (<15%) is the key to controlling an infestation within a building.  Some infestations are promoted in buildings due to poor maintenance.  

Parasites which affect the common furniture beetle

There are some parasitic insects which feed on the common furniture beetle for instance:  Korynetes caeruleus is a member of the Cleridae family. A common predator of Death Watch Beetle it also attacks Anobium. The larva of this steely blue beetle grows to 14mm and moves slowly around Anobium tunnels hunting out and devouring the wood-eating larvae.

Pediculicides venti-icosus (grain Itch-Mite) has been found living within the larval bore dust of active common furniture beetle (A.punctatum) infestation and it causes server dermatitis in humans. This large occurrence was recorded in detail in France. Due to global warming is could occur in the UK.

Action

It is sensible to have a suitably qualified person inspects the timber as the woodworm exit holes will remain for the life of the building.  Therefore, the infestation could be 30 to 200 years old or it could be recent.  Testing for activity requires witness tabs to be installed followed by long term monitoring.  In some cases, the timbers may be treated with insecticide to control an infestation.

Nigel Foster