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 bores into wood.

Some arrive unseen and feed on the reverse of the canvas. Others inhabit linings, consuming 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 discovered only once damage is 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 and treatment approach. They do not typically require anoxic eradication, but they do demand accurate identification, targeted intervention, and consistent environmental control.

The damage they cause can be irreversible. In many cases, however, it is preventable.

Distinction from Wood-Boring Insects

Anoxic treatment remains the appropriate response for wood-boring insects such as Anobium punctatum and drywood termites, whose larvae develop within timber elements and are inaccessible with surface treatment.

The insects considered in this article 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 crucially, they are accessible—both to inspection and to targeted intervention.

This does not make them less serious. A prolonged cockroach infestation can significantly weaken a canvas and introduce corrosive staining. Carpet beetle larvae can undermine linings over extended periods. Silverfish can reduce surface coatings and sizing layers to nothing.

The difference is not severity, it is method.

Species at a Glance

Species	Common Name	Primary Targets	Damage Signature	Primary Response
Periplaneta americana / Blatta orientalis	American / Oriental Cockroach	Verso canvas, glue sizing, paper backings, organic debris	Faecal spotting, grease deposits, egg cases, surface abrasion	Environmental management, exclusion, pesticide gel
Blattella germanica	German Cockroach	Sizing, starch, any organic residue	Faecal trails, surface grazing, distinctive egg cases	Exclusion, baiting, targeted application
Lepisma saccharina	Silverfish	Glue, starch, paper, canvas fibres, natural varnish	Irregular surface grazing, ground layer loss, paper thinning	Environmental desiccation, sticky traps, freezing
Thermobia domestica	Firebrat	Glue, starch, canvas, paper	Similar to silverfish; favours warm, humid areas	Heat/humidity reduction, trapping
Anthrenus verbasci / Attagenus unicolor	Varied / Black Carpet Beetle	Canvas (linen), wool linings, natural fibre supports	Irregular holes in canvas weave; cast larval skins	Freezing, trapping, environmental management
Tineola bisselliella	Webbing Clothes Moth	Wool, natural fibre canvas; occasionally varnish	Fibre consumption; silken tubes and frass	Freezing, pheromone traps, storage hygiene
Liposcelis spp.	Booklice (Psocids)	Mold, starch paste, paper	Surface grazing; indicator of elevated humidity and mold	Humidity reduction (primary); trapping

Cockroaches: The Verso Threat

In South Florida, cockroaches are among the most prevalent and damaging pests affecting paintings.

The American cockroach (Periplaneta americana) and the Oriental cockroach (Blatta orientalis) are most frequently encountered in gallery and storage environments, though the German cockroach (Blattella germanica) is common in interior spaces.

Cockroaches are opportunistic omnivores, drawn particularly to the verso of paintings where sizing, adhesives, and accumulated organic residues provide a stable food source. Activity is concentrated in dark, undisturbed areas—behind stretched canvases, within frame rebates, and along stretcher channels.

Damage presents in three principal ways:

• Consumption of sizing and fibres, leading to localised structural weakening
• Deposition of frass, which is acidic, staining, and capable of migrating through the support
• Placement of oothecae, or egg cases, within sheltered structural elements

The most persistent issue is visibility. Damage develops on the verso and may remain undetected until it begins to affect the paint layer.

Routine inspection of the recto rarely captures this. Turning the work over does.

Silverfish and Firebrats: Progressive Surface Loss

Silverfish (Lepisma saccharina) and firebrats (Thermobia domestica) are widespread across climates and highly adaptable.

Their relevance lies in their diet. They target starches, glues, and cellulose—materials integral to the structure of most paintings. Sizing layers, animal glues, lining adhesives, and even the canvas itself are all viable sources.

Damage is typically slow and cumulative. Rather than perforation, they produce a progressive thinning of material—subtle, irregular grazing that often goes unnoticed until at advanced stages.

Under raking or UV light, affected areas may appear matte, slightly recessed, or disrupted in surface continuity.

Their presence is strongly linked to elevated relative humidity. Without addressing environmental conditions, treatment alone is unlikely to be effective.

Carpet Beetles: Fibre and Protein Consumers

Carpet beetles (Anthrenus spp., Attagenus unicolor) are among the most persistent museum pests globally.

It is the larval stage that causes damage. Larvae are keratin feeders, targeting wool, hair, and other animal-derived materials. In paintings, this most often affects wool or mixed-fibre linings, though protein-based media and ground layers may also be vulnerable.

Damage is typically internal to the lining structure—channels, voids, and thinning of fibres—often accompanied by cast skins and frass.

Freezing can be effective where appropriate, but it is not a universal solution. Acrylic paint films, in particular, present risk due to glass transition behaviour at low temperatures. Each work must be assessed individually.

Freezing can be a tool, not a default.

Booklice: Environmental Warning Sign

Booklice (Liposcelis spp.) are less directly damaging than other pests but are diagnostically important.

Their presence indicates elevated relative humidity and active or recent fungal growth. They feed on mold and starch-based materials and will colonise the verso of canvases, frames, and backing materials.

The concern is not the insect itself, but the environment it signals.

If booklice are present, the conditions for mold are already in place.

Treatment is therefore primarily environmental. Reducing RH below 55% will typically eliminate the infestation. Without that correction, recurrence is likely.

Identifying Active Infestation

Distinguishing between historic and active infestation is critical. Many works carry residual evidence—frass, minor loss, or staining—that does not indicate ongoing activity. Misdiagnosis leads to unnecessary treatment or, worse, missed intervention.

Inspection should prioritise the verso, examined under raking light. Frame rebates, stretcher channels, and backing elements require close attention.

Indicators of active infestation include:

• Live insects or larvae
• Fresh, unconsolidated frass
• Intact oothecae, or egg cases
• Recent or progressing surface loss

Where activity is confirmed, isolation is immediate and non-negotiable.

Treatment: Integrated Pest Management

There is no single treatment solution.

Effective response combines isolation, targeted intervention, environmental control, and ongoing monitoring—Integrated Pest Management (IPM).

Isolation is always the first step. Containment prevents spread and allows controlled assessment.

Treatment varies by species. Freezing may be appropriate in select cases. Traps and monitoring systems provide both control and data. Chemical treatments should be used cautiously and never in direct contact with works.

Environmental correction underpins everything. Without it, treatment is a temporary solution.

Prevention and Cyclical Maintenance

Prevention is straightforward in principle and difficult in practice.

Regular inspection—particularly of the verso—is the most effective early warning system. Environmental stability, especially maintaining RH between 45–55%, reduces the likelihood of infestation.

Storage conditions matter. So does discipline.

Incoming works should be quarantined. Organic packing materials should be monitored. Records should be maintained.

Most failures in pest management are not technical. They are procedural.

South Florida: Elevated Risk

South Florida presents near-ideal conditions for pest activity: warmth, humidity, and no true dormancy period.

Cockroaches are ubiquitous. Silverfish and booklice thrive where climate control is inconsistent. Carpet beetles are routinely encountered.

Collections in residential or non-purpose-built environments are particularly vulnerable.

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

The ArtCare Approach

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 environmental correction.

Not every infestation requires extensive treatment. Some require monitoring. Others require decisive action.

The value lies in knowing the difference early.

If you have a project you’d like us to assess, or you need advice on our wide portfolio of conservation services, drop us a line and we’ll be happy to discuss.