Silent Threat: ArtCare’s Guide to Anoxic Treatment for Insect Pest Eradication in Paintings on Canvas and Panel

Not every insect that threatens a painting does so by boring into wood.

A significant number of the most persistent pests operate at the surface or within the layered structure of the object itself. Some arrive unnoticed and establish activity on the reverse of the canvas. Others inhabit linings, feeding on starch- and protein-based sizing, or settle into the voids between stretcher members and corner joins. What they leave behind—frass, cast skins, egg cases, and staining—is often only identified once damage is already well established.

This case study focuses on the insect species most commonly encountered in paintings on canvas and panel outside of wood-boring infestations: cockroaches, silverfish, carpet beetles, and booklice. These pests require a different diagnostic approach and a more targeted form of intervention. They do not typically require anoxic eradication, but they do demand accurate identification, proportionate treatment, and, critically, consistent environmental control. While the damage they cause is often irreversible, in many cases it remains preventable with early identification and appropriate management.

Wood-boring insects remain a separate category. Anoxic treatment is the appropriate response for species such as Anobium punctatum and drywood termites, whose larvae develop within timber elements and are largely inaccessible to surface treatment. The insects considered here differ in two key respects. They are primarily surface or interface feeders, consuming sizing, adhesives, fibres, and organic residues rather than excavating within solid wood, and they remain accessible—both to inspection and to targeted intervention. This distinction does not reduce their significance; rather, it defines the method by which they must be addressed.

Prolonged cockroach activity can significantly weaken a canvas while introducing corrosive staining. Carpet beetle larvae are capable of undermining linings over extended periods, often without immediate visibility. Silverfish can progressively reduce surface coatings and sizing layers to nothing. The issue is not one of severity, but of how the damage develops and how it must be identified and treated.

Species at a Glance

In South Florida, cockroaches represent one of the most prevalent and consistently damaging risks to paintings. American cockroaches (Periplaneta americana) and Oriental cockroaches (Blatta orientalis) are most commonly associated with building infrastructure, storage environments, and damp service spaces, while German cockroaches (Blattella germanica) are more typically linked to occupied interior environments such as kitchens and staff areas. In practice, particularly in warm and humid climates, these distinctions are less defined, and all three species may be encountered within gallery and storage environments where conditions allow.

Cockroaches are opportunistic omnivores, drawn to the verso of a painting where sizing, adhesives, and accumulated organic residues provide a stable and often undisturbed food source. Activity tends to concentrate in dark, protected areas—behind stretched canvases, within frame rebates, and along stretcher channels—where access is easy and disturbance minimal. The resulting damage develops through a combination of material consumption and contamination. Sizing and fibres are gradually consumed, leading to localised structural weakening, while acidic frass introduces staining that may migrate through the support. Egg cases are frequently deposited within sheltered structural elements, embedding the infestation within the object itself and increasing the likelihood of persistence if not properly addressed.

A central challenge is that this activity is largely concealed. Damage develops on the verso and may remain undetected until it begins to affect the paint layer. Routine inspection of the recto alone is insufficient; periodic examination of the reverse is essential in identifying early-stage activity and preventing more significant deterioration.

Silverfish (Lepisma saccharina) and firebrats (Thermobia domestica) are widespread and highly adaptable, and their relevance lies in their diet. Both species target starches, glues, and cellulose—materials that form the structural basis of most paintings. Sizing layers, animal glues, lining adhesives, and even the canvas itself are all vulnerable.

Damage caused by these insects is typically slow and cumulative. Rather than producing discrete perforations, they create progressive thinning through irregular grazing, often going unnoticed until it is well advanced. Under raking or ultraviolet light, affected areas may appear matte, slightly recessed, or disrupted in their surface continuity, providing one of the few early indicators of activity. Their presence is closely linked to elevated relative humidity, and without addressing environmental conditions, treatment alone is unlikely to be effective.

Carpet beetles, including species within the genera Anthrenus and Attagenus, are among the most persistent pests encountered in both museum and residential contexts. It is the larval stage that causes damage. These larvae are keratin feeders, targeting wool, hair, and other animal-derived materials, which in paintings most often translates to wool or mixed-fibre linings, though protein-based media and ground layers may also be affected.

Damage is typically internal to the lining structure, developing as channels, voids, and areas of fibre loss that may not be immediately visible from the surface. Evidence often includes cast larval skins and fine deposits of frass, though these may remain concealed within the lining itself. Freezing can be an effective treatment in certain cases, but it is not universally appropriate. Materials such as acrylic paint films introduce additional risk due to their behaviour at low temperatures, and each work must therefore be assessed individually before treatment is undertaken.

Booklice (Liposcelis spp.) are less directly damaging but remain diagnostically significant. Their presence is strongly associated with elevated relative humidity and with active or recent fungal growth. They feed on mold and starch-based materials and tend to colonise the verso of canvases, frames, and backing elements.

The concern in this case is not the insect itself, but the conditions it indicates. Where booklice are present, the environment is already suitable for mold development. Treatment is therefore primarily environmental. Reducing relative humidity below approximately 55% will typically eliminate activity, whereas failure to address the underlying conditions will almost certainly result in recurrence.

Distinguishing between historic and active infestation is critical. Many works carry residual evidence—frass, minor losses, or staining—that does not indicate ongoing activity. Misinterpretation can lead either to unnecessary intervention or to overlooked risk.

Inspection should prioritise the verso of the work and be carried out under appropriate lighting conditions, including raking light where possible. Frame rebates, stretcher channels, and backing elements require close and methodical examination. Indicators of active infestation include live insects or larvae, fresh and unconsolidated frass, intact egg cases, and evidence of recent or progressing loss. Where activity is confirmed, isolation must be immediate to prevent further spread.

Effective treatment is based on an integrated pest management approach, combining containment, targeted intervention, environmental correction, and ongoing monitoring. There is no single solution. Freezing may be appropriate in select cases, while traps and monitoring systems provide both control and useful data. Chemical treatments should be used cautiously and never applied directly to the work without careful consideration. As with all pest-related issues, environmental control underpins any successful outcome; without it, treatment remains temporary.

Prevention is straightforward in principle but requires consistency in practice. Regular inspection—particularly of the reverse of the work—remains the most effective early warning system. Maintaining relative humidity within a stable range of approximately 45–55% significantly reduces risk, while appropriate storage conditions, handling protocols, and procedural discipline all contribute to long-term protection.

Incoming works should be quarantined and assessed before integration into a collection. Organic packing materials should be monitored, and accurate records maintained. In practice, most failures in pest management are procedural rather than technical.

South Florida presents near-ideal conditions for sustained pest activity, with warmth, elevated humidity, and no true dormancy period. Cockroaches are ubiquitous, silverfish and booklice thrive where climate control is inconsistent, and carpet beetles are routinely encountered. Collections housed in residential or non-purpose-built environments are particularly vulnerable, and in this context, inspection becomes an essential part of ongoing care.

ArtCare Conservation provides pest assessment and management across its Miami, New York, and Los Angeles studios. For wood-boring insects requiring anoxic treatment, separate protocols apply. For the species discussed here, the approach centres on accurate diagnosis, proportionate intervention, and sustained environmental control.

Not every infestation requires extensive treatment. Some require monitoring, while others demand immediate and decisive action. The value lies in recognising the difference early and responding accordingly.