With this article and related ones we try to understand how to solve and prevent the problem due to the presence of woodworms.
Recognizing a woodworm
Under the generic name of “woodworms” are included various species of insects, united by the fact that they eat wood and for this reason they are called xylophagous or “wood eaters”.
The “woodworms” most commonly found in our homes include various species of beetle insects:
- the Anobidae,
- the Lyctides,
- the Cerambicides.
These, at the larval stage, are able to settle inside the wood by digging long tunnels and, inside these tunnels, complete their biological cycle to become adult insects.
The larvae of woodworms feed on the wood, or better, on the cellulose contained in it, and for this reason they can seriously compromise the aesthetics and the integrity of a wooden structure or of a piece of furniture.
Once completed the metamorphosis from larva to adult, the woodworms flicker and turn outwards, coming out from the wood, looking for a partner of opposite sex with which to reproduce.
During the flicker phase the adults create a small round hole in the wood. These holes, called flicker holes, represent the end of the tunnels dug by the larvae and are the indistinguishable sign of a woodworm infestation. From the size and shape of these holes it is possible to recognize the species.
Another indistinguishable sign of a woodworm infestation is the woodworm rust or sawdust, which is nothing more than the result of the excavation of the larvae. The burn is composed of the lignin discarded by the larva, because it is free of cellulose, and its excrements. This sawdust is pushed out by the adult insects during the final phase of abandonment of the wood.
The presence of this burn is a clear sign of an infestation still in progress.
The adult woodworm will then lay its eggs again in the fissures of the wood, giving rise to a new infestation of larvae that will in turn dig new tunnels.
Let’s see below what are the characteristics of the three types of woodworm mentioned above.
The Anobium punctatum (Anobium punctatum), are small woodworms, 4 to 6 mm long when adult, which preferably damage seasoned and bark-free wood including plywood. The attack to the wood is generally superficial and therefore hardly compromises the stability of a structure.
The larvae develop for 2-4 years, in which they continue to erode the wood incessantly. Humidity of less than 40% blocks their development.
Adults appear in the spring and survive only a few days and can often be found near windows because they are attracted by light. Females lay between 20 and 40 eggs.
The species Xestobium rufovillosum is a larger anobid than the previous one (7 mm) and develops preferably in damp woods already affected by fungi. The larvae can take up to 10 years to complete the cycle and, in case of massive infestations, can compromise the stability of the structures.
This species produces a “noise” similar to the ticking of a clock, which is a reminder produced by the male by percussion on the walls of tunnels, and for this reason it is called “death clock”.
Lyctids (Lyctus linearis, Lyctus brunneus) are very common species of small size (3-5 mm) that preferably attack new woods, parquet, and skirting boards. Adults stay alive for up to three weeks and females lay about 20 eggs.
The development period of the larvae is usually 12 months and, as for the Anobians, they feed on wood forming small holes when the adults leave the galleries dug by the larvae.
To the Cerambicids belong the species Hylotrupes bajulus and Trichoferus holosericeus which are known with the generic name of house capricorn. The adults are much larger and measure 17-25 mm, as well as the larvae that measure 22-25 mm.
This woodworm is definitely the most dangerous and can do the most damage.
Hylotrupes bajulus attacks the coniferous woods, attracted by the resins, whilst the cases of attacks on hardwoods of broad-leaved trees are to be traced back to the species Trichoferus holosericeus, whose larva, among other things, is very similar.
The female appears from mid-June to the end of August and after mating she lays her eggs in the galleries dug by the larvae thanks to the long ovipositor.
The larvae dig very wide tunnels, up to 1 cm in diameter, and in depth. Their biological cycle can last very long depending on the temperature and humidity values of the environment, even up to 17 years! For this reason it can be difficult to notice an infestation in progress. The mechanical resistance of load-bearing structures such as beams can be seriously compromised by the action of these woodworms, until they collapse.
Signs of woodworm presence
Woodworms are not necessarily noisy and, on the contrary, the most common ones, pierce the wood and feed without causing any noise.
The only species that can be traced back to the noise produced are the “House Capricorn”, whose larvae produce a certain noise while feeding, and the “Death Clock” which produces a rhythmic ticking caused by the percussion of the adult insect inside the tunnels. All the other woodworms feed silently.
The holes in the wood are one of the most obvious signs of infestation. But the presence of holes, in the absence of rosemary, does not necessarily indicate an infestation in progress. In fact, the holes could derive from an old infestation or from a defect in the wood.
In general, if the holes have a certain amount of sawdust or rosume inside them, the infestation is still in progress.
Anobians and Lyctids cause small holes up to a maximum of 2 mm in diameter, while the capricorn in the houses causes much larger holes of about 5 mm in diameter.
The rosemary is a characteristic sign of an infestation in progress, even if often it may not be observed as it is eliminated during the cleaning operations. However, it is always useful to shake the wooden artefact to see if roses caused by woodworms are coming out of it.
The adults of woodworms usually flicker, mate and live a few days. They can also be found dead near the windows of infested houses because, attracted by daylight, they are used to fly towards the brightest windows.
Environments favourable to woodworm
From an environmental point of view, woodworms do not require any special conditions for their development, provided that the wood or cellulose that forms the larvae’s feeding substrate is present.
The ecological role of xylophagous insects in nature is easily intuitable: they have the task of decomposing the cellulose and wood of dead plants by decomposing this biological material in order to avoid its accumulation in the environment and obtaining nourishment for their sustenance.
In nature there are many insects able to operate as xylophagous but only some of them actually represent a risk for the wood in place or for the furniture.
In fact, most xylophagous attack the wood with a certain degree of humidity or even rotting. Only a few xylophagous are able to attack drier woods such as those used in construction and carpentry.
The degree of humidity, therefore, greatly influences the persistence and development of these insects. Wooden materials placed in humid environments are certainly more exposed to potential attacks by woodworm and it is for this reason that the environments most at risk are taverns, wine cellars, old houses in historical centres or little used houses (country and mountain houses), museums, archives and libraries if they are not properly ventilated and dehumidified.
It should also be remembered that paper, being in fact made from cellulose, is a very popular material for xylophagous insects, as can occasionally be the natural fibers of vegetable origin from which some fabrics are made (linen, hemp, bamboo).
How woodworm arrive
Usually woodworm enter the houses by transporting already contaminated objects such as wooden antiques or second-hand furniture and equipment.
In some cases woodworm, being insects that normally live also in the external environment, can move from external environments to the inside of houses and start a new infestation.
Health risks due to woodworm
The presence of woodworm alone in a house does not directly represent a danger to people’s health.
However, it is important to know that, together with woodworm, there are often other arthropod parasites of larvae or woodworm adults that can cause stings through accidental contact with people’s skin. These are two woodworm parasitoids that are worth getting to know better.
The Pyemotes ventricosus mite or Woodworm mite, has a stinging and sucking apparatus with which it affects adult insects (beetles or lepidoptera and in particular woodworms) and injects a toxin that paralyses the victim and slowly digests the tissues so that the mite can feed on it.
These mites, if they are present because of the insects that infest the environments frequented by humans (woodworms), can target people by causing stings on both covered and uncovered parts of the body.
Usually the result is papules in relief surrounded by a rosy halo with a live blister in the center. The lesion can take on a typical “comet” (link) appearance due to the effect of the neurotoxin injected by the Mite.
The Scleroderma domesticum or simply Scleroderma is a small parasitoid, very small (1-2 mm long, 1 mm wide), which lives and develops at the expense of Coleoptera and Lepidoptera larvae.
Being wingless and dark brown in colour, the scleroderms may be mistaken for very small ants even if very often their presence goes unnoticed.
The females are equipped with a poisonous abdominal spine which they use to paralyze the larvae of the host insects. Accidental contact with these insects (in the presence of furnishings, wood on site or storage wood infested with xylophagous beetles such as woodworms) can cause very painful stings.
The sting generally causes localized ponfi, and often causes pain when inflicted, and in cases of hypersensitivity of the subjects can cause widespread swelling and even fever. link
Prevention of woodworm infestations
At an environmental level the presence of woodworm can be avoided by first of all acting on the humidity of the rooms, which must be kept as low as possible.
Obviously, where there is a lot of wooden material, and especially in the presence of ancient objects, the risk of infestation by these insects becomes high. In these cases it would always be advisable to carry out preventive antitarlo treatments, especially if there are valuable materials to defend.
These treatments generally consist in treating the surface of objects with insect repellent substances in order to prevent the female woodworm from laying on the wooden surface giving rise to an infestation.
Woodworm control systems
In the case of wooden objects of small size or otherwise of little commercial value, preventive treatments with antitarlo or curative with specific insecticides can also be conducted independently.
Do-it-yourself systems, on the other hand, are not recommended in the case of structures on site (ceilings, mezzanines, beams, etc…) or valuable furniture and objects.
It is necessary to resort to specialized interventions that are based on the use of sophisticated systems for the treatment of the structures, and among these the most widespread are through the use of machinery for the treatment with microwaves (heat treatment), or chambers for the treatment in modified atmosphere.
It is clear that none of these treatments can resolve any damage caused by woodworm damage that will be required in case of restoration work. Moreover, pest control treatments do not protect against subsequent attacks, so they must always be combined with anti-worm treatments to prevent a new infestation.
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