Introduction
The discovery of small, fresh, conical piles of sawdust in your home can provoke one of those ‘sick in the stomach’ feelings. Wood borers!
All borers will do some kind of damage to timber, but all is not lost – there are ‘good borers’ and ‘bad borers’. You need to be aware of the differences between the two groups, because ‘good borer’ damage will be cheap to repair, but it may be expensive to repair the damage done by ‘bad borers’.
The ‘good borers’ are beetles whose damage is limited to the first five years after the timber was milled. They attack mainly soft wood or moist decaying timber, and the damage done to the wood is superficial; it can be fixed by filling with putty and a quick repaint.
The ‘bad borers’ are beetles that can attack hardwood or softwood of any age. The damage is often structural, requiring complete replacement of the timbers, which are often floor boards or major support beams.
GOOD BORERS
Ambrosia or Pinhole Borer Beetle
The Ambrosia or Pinhole Borer, Platypus australis, belongs to the Curculionidae family and has a biology that differs from most other wood borers. In other wood-boring beetles, it is the larvae (grubs) that bore through the wood and create the galleries. In the case of the Ambrosia Beetle, the adult female bores into the timber, creating a central tunnel with side branches. The larvae do not feed on the wood; they eat the fungus that grows on the moist timber gallery excavated by the adult female. The fungus causes a staining of the wood, which is characteristic of Ambrosia Beetle attack. Since the fungus the larva feeds on requires a moist environment, attack is confined to living or recently felled timber. Damage is only superficial.
The Ambrosia or Pinhole Borer Beetle, Platypus australis
Photographer: Kate Sparks, Source: Museum Victoria
Dampwood Borer
The Dampwood Borer, Hadrobregmus australiensis, belongs to the Anobiidae group of borers. It is a comparatively large beetle that attacks both softwoods and hardwoods, but only wood that is moist or decayed by wood-rotting fungi. As such, the wood affected by the borer is already damaged and therefore the borer is not considered to initiate damage. Typically in a household situation, damp-affected wood occurs in the subfloor parts of the building. Once the decayed wood has been removed and the reason for the damp condition is fixed, no further Dampwood Borer damage will occur.
The Dampwood Borer, Hadrobregmus australiensis
Photographer: Kate Sparks, Source: Museum Victoria
Wood damage by Dampwood Borer
Photographer: Kate Sparks, Source: Museum Victoria
Longicorn beetles
These are the cerambycid or longicorn beetles, so named because of their long antennae. Most species attack living trees. The boring is done by the larva (beetle grub), which may take 1–3 years to complete its development. Sometimes, the live tree that was originally attacked may have become part of a house or made into furniture, and the owner can get quite a surprise when a large beetle emerges. Damage is only superficial.
A longicorn beetle, Phoracantha sp.
Photographer: Kate Sparks, Source: Museum Victoria
Powder Post Beetle
This lyctid borer attacks the sapwood of susceptible hardwoods, but not softwoods. The female lays her eggs in the exposed end-pores of freshly cut wood, or in a living tree that has been damaged. Borer attack is confined to about the first five years following felling of the logs, or when the timber moisture drops below 20%. The larvae feed along the grain of the wood and never attack the heartwood, so the damage is superficial.
Exit holes of the Powderpost Beetle
Photographer: Kate Sparks, Source: Museum Victoria
Particoloured Auger Beetle
The auger beetles are bostrichid borers. They attack only recently felled logs and green timber, and only the sapwood of hardwood and softwood is susceptible to attack. The larvae feed along the grain of the wood, so the damage is superficial. The larvae (beetle grubs) produce a fine powdery frass (insect poo). The Particoloured Auger Beetle, Mesoxylion collaris, is the most frequently encountered species. It often bores its way out through the plasterboard during the first summer after a house has been constructed or renovated.
The Particoloured Auger Beetle, Mesoxylion collaris
Photographer: Kate Sparks, Source: Museum Victoria
BAD BORERS
Wood-boring Weevil
This beetle, Pentaminus rhyncoliformis, belongs to the Curculionidae or weevil group of beetles. It attacks only softwoods, such as pine skirting boards. However, unlike the larvae of the ‘good borers’, which feed along the grain, the larvae of the Wood-boring Weevil meander throughout the wood, producing a honeycomb of tunnels that destroys the integrity of the timber.
The Wood-boring Weevil, Pentaminus rhyncoliformis
Photographer: Kate Sparks, Source: Museum Victoria
‘Honeycomb’ damage cause by larvae of the Wood-boring Weevil
Photographer: Kate Sparks, Source: Museum Victoria
Furniture Beetle
The beetle, Anobium punctatum, is an anobiid borer and can cause serious structural damage to timber. Attack occurs mainly in softwoods used in areas such as flooring, panelling and furniture. Unlike the ‘good borers’, this beetle can attack old dry wood. The female lays eggs in cracks and crevices or abraded areas in the timber, and the larval period may take several years. The reason it can cause serious damage is that the larvae feed in a meandering manner, producing a honeycomb of tunnels through the wood and destroying the structural integrity of the timber.
The Furniture Beetle, Anobium punctatum
Photographer: Kate Sparks, Source: Museum Victoria
‘Honeycomb’ damage caused by larvae of the Furniture Beetle
Photographer: Kate Sparks, Source: Museum Victoria