Silent Threats: Insect Pest Eradication and Damage 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 and damaging 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 created by stretcher members and corner joins. What they leave behind—frass, cast skins, egg cases, and staining—is often only discovered once damage is already well established.

This guide 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.

Wood-boring insects, including Anobium punctatum and drywood termites, remain a separate category. Their larvae develop within timber elements and are largely inaccessible to surface treatment, making anoxic intervention or structural replacement the appropriate response.

The insects discussed here differ in two important respects. They are surface or interface feeders, consuming sizing, adhesives, fibres, and organic residues rather than excavating within solid wood. Just as importantly, they remain accessible—both to inspection and to treatment. This accessibility, however, should not be mistaken for reduced risk. Cockroach infestation can significantly weaken a canvas while introducing corrosive staining. Carpet beetle larvae can undermine linings over extended periods. Silverfish are capable of progressively reducing surface coatings and sizing layers to nothing. In each case, damage tends to develop gradually and often out of view, which increases the likelihood of late detection.

Case Study on Vizcaya Museum and Gardens Galleon Room Italian Landscapes 

In South Florida, cockroaches are among the most prevalent and potentially damaging pests affecting 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, this distinction is 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 in several ways. Consumption of sizing and fibres leads to localised weakening of the support, while the deposition of acidic frass can introduce staining that may migrate through the canvas and affect the paint layer. Egg cases (oothecae) are frequently deposited within sheltered structural elements, embedding the infestation within the object itself and increasing the likelihood of recurrence if not properly addressed.

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

Silverfish (Lepisma saccharina) and firebrats (Thermobia domestica) are widespread and highly adaptable, and their relevance in a conservation context lies primarily in their diet. Both species target starches, glues, and cellulose—materials that are integral to the structure 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 clear perforations, they create progressive thinning through irregular grazing. This form of loss often goes 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 visual indicators of activity.

Their presence is closely linked to elevated relative humidity, and without correcting the environmental conditions that support them, treatment alone will rarely be effective. In this respect, they are as much an environmental indicator as they are a direct cause of damage.

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

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 skins and fine frass deposits, though these may be concealed within the structure of the lining itself. As with other pests, the damage tends to be progressive and is frequently only recognised once structural integrity has already been compromised.

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 materials.

The concern in this instance is not the insect itself, but the environment it indicates. Where booklice are present, conditions suitable for mold growth are already established. Treatment therefore becomes 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. Misdiagnosis in either direction can lead to unnecessary intervention or, conversely, to missed 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 the presence of live insects or larvae, fresh and unconsolidated frass, intact egg cases, and evidence of recent or progressing loss.

Where activity is confirmed, isolation should be immediate. Effective response combines containment, targeted intervention, environmental correction, and ongoing monitoring within an integrated pest management framework.

Isolation prevents spread and allows for controlled assessment. Treatment strategies vary depending on species and extent of infestation. Freezing may be appropriate in certain cases, while traps and monitoring systems provide both control and useful data. Chemical treatments should be used with caution and should never be applied directly to the work without careful consideration.

Environmental correction underpins all successful treatment. Without it, intervention is temporary.

Prevention, while straightforward in principle, requires consistency in practice. Regular inspection—particularly of the verso—remains the most effective early warning system. Maintaining relative humidity within a stable range, ideally between 45–55%, significantly reduces risk. Storage conditions, handling protocols, and procedural discipline all play a role.

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. In this context, inspection is not optional; it is essential.

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 appropriately.