Pest control: The big crawl

As is well known, the tasks of museums include exhibiting, preserving, researching, collecting and communicating. But more and more people are saying that museums are failing to preserve and that collections are under threat from pests. A conversation with museum conservators and pest control experts shows that this is not the case.

One of the regular tasks of conservators in collections is to check for pest infestation. This is because contamination with pests such as moths, beetles or even paperfish can cause major damage to art objects and artifacts. For insects, museum collections represent one thing above all else: Food. Only around 30 pests pose a threat to our collections in museums, libraries and archives. A visit to the Museum Fünf Kontinente shows what the work of conservators Carolin Binninger and Jessica Bekesi looks like in practice. As an ethnological museum with its diverse treasures made from a wide variety of materials, it is a veritable land of milk and honey for museum pests. Many objects are made of organic materials such as wood, leather, fur, feathers and even bones. The first step is packaging and storage, where an attempt is made to keep the objects as sealed as possible. The restorers also ensure that the objects are sorted by material within the region of origin. Particularly sensitive objects are also stored in separate storage units.

Another important tool is the regular inspection of the exhibitions and depots. The conservators keep an eye out for flying insects, beetles and other potential pests and check the UV and glue traps. In addition, parasitic wasps are used to decimate the larvae of museum pests. The ichneumon wasps are regularly released for this purpose. This is mainly done in the warmer months. Due to climate change, this treatment has become much more frequent and the period in which it takes place has also become longer. However, the conservators emphasize: “It is difficult to minimize, or at best eliminate, the risk of damage to all objects equally, because an effective measure can be optimal for one substance and unsuitable for another, which is particularly true for combinations of materials on objects. Where it is not possible to treat entire groups of materials, the best possible concept for preserving the object is determined and implemented on a case-by-case basis. In general, we try to make it as unattractive as possible for pests to stay indoors and feed.” The two conservators have observed that discussions on the subject of pests in museums are currently very heated in some cases. Infestations are often presented as a lack of hygiene or control, which could be one reason, according to the experts, but there are many other reasons why pests appear in collections. They emphasize that conservators are very aware of the topic due to their studies. One focus during specialist training is therefore particularly on preventative measures or reacting quickly and professionally in the event of contamination in order to ensure the preservation of the objects.

In doing so, the museum staff are also following the recommendations that the Dutch Institute for Cultural Heritage published in a guide in 2007. The five steps of Integrated Pest Management (IPM) are explained there, because for a long time the use of insecticides was the main method. However, this has many disadvantages. For one thing, the pests developed resistance over time, which led to the use of more toxic substances that were also harmful to employees. Another problem was that they could also damage the objects in the collection. The experts therefore set about looking for alternative options and developed new safe and clean strategies to protect collections from pest infestation. They developed the IPM with five measures to be taken: avoid, block, detect, restrict and treat. Treatment is the last step to be taken, which should also use methods that protect people, the environment and materials. Non-toxic control methods are therefore primarily required, as toxic methods should only be considered as a last resort.

Ideally, however, treatment that leads to the death of the pests is not necessary because measures have already been taken in advance to prevent infestation. Preventive measures and their control should be the focus of IPM. The first step is avoidance, which includes making it as unattractive as possible for insects to stay in the museum rooms. The first adjustment screw is the room climate, so the humidity should be below 65 percent and the temperature below 18 degrees. Sufficient ventilation must also be ensured to prevent the development of a microclimate. There are also a few points to bear in mind when furnishing the rooms; for example, it is recommended that shelves, display cabinets, cupboards and other furniture are positioned at right angles to the outer walls. There should also be a gap of 15 centimeters between the floor and the lower shelves, as this provides a natural barrier. The next step is blocking; insects should be prevented from entering the building as far as possible. There are many ways to do this: damage to the building is a gateway, but entrances for visitors and employees also offer opportunities for entry. In addition, visitors should not be allowed to take their jackets and bags into the exhibition rooms if possible, as this can also introduce pests unintentionally. Packing materials and incoming objects pose further dangers. Regular inspections of the collection and storage rooms for signs of pest infestation serve the third step of IPM, namely detection. A variety of measures can be taken here.

In addition to museums, archives also have to contend with pest infestations. The IPM is also used there, as the company APC informs us. In the case of the state archives in Duisburg, the company was commissioned to take preventive action. Archives are particularly affected by paperfish due to their collection area. The company’s measures then concentrated on this area. First of all, a quarantine zone is set up, which is separated from other areas. The newly arrived archive materials are initially stored there and the company also freezes them. Care must be taken to ensure that they are not exposed to frost, as this could damage the archives. The conservators at the Museum Fünf Kontinente use a similar procedure. New additions to the collection are always sent into quarantine, regardless of which households or collections they come from, as restorer Carolin Binninger emphasizes. It cannot be ruled out that harmful insects such as clothes moths or silverfish may be found, but as a collector you only have limited influence on this. The new objects for the collection are also frozen where possible and Binninger and Bekesi also rely on anoxic treatment, which they carry out prophylactically.
The actual monitoring only begins after quarantine. In the case of the National Archives, monitoring is carried out using sticky floors with a protein source as an attractant for the insect pests, according to the company APC. When deploying the traps, locations are primarily chosen that are close to where the pests are hiding. The company’s experts check the traps at set intervals. The restorers at the Museum Fünf Kontinente follow a similar procedure. Adhesive traps are used here too, but they also use UV traps, which they check regularly.

If an infestation does occur despite all precautionary measures, the authors of the guide recommend restricting it. The affected objects must be identified and isolated. In addition, the source must be found and removed. If these measures are unsuccessful, the final step is treatment. There are two methods for this: physical, non-toxic treatment and toxic, chemical treatment. It should be noted that the latter can react with the materials and cause damage due to the solvents and additives they contain. Physical, non-toxic methods are therefore preferable. Two proven methods are heat treatment and nitrogen fumigation, as we learned from Rentokil, a company specializing in pest control.

During heat treatment, the pests are exposed to high temperatures, which denature the proteins and enzymes in their bodies and lead to the death of the insects. For the procedure, the art objects or artifacts are placed in a room specially designed for heat treatment. There, the temperature is raised slowly and in a controlled manner to between 50 and 60 degrees. The temperature is selected in such a way that it kills the pests but is not harmful to the objects. In order to guarantee the death of all pests, the art objects are treated in the heat chamber over a longer period of time. The duration depends on the type of pests, the thickness of the materials and other factors. At the end of the process, the temperature is slowly lowered back to normal to prevent damage to the objects. The permanent control of temperature and humidity during the entire treatment is carried out extremely carefully to avoid exposing the works of art to unnecessary stress. The particular advantage of this method is that it leaves no toxic residue and can be used on many materials such as wood, textiles, paper and organic substances, according to an expert from the company.

Conservator Carolin Binninger from the Museum Fünf Kontinente in Munich tells us that heat treatment is not used for the objects in the museum’s collections. She points out that heat treatment can put a strain on many materials. She tells us that the application of high temperatures means a high energy input, even with strict controls. This is particularly important for objects made of different materials. The main reason for this is that each material reacts differently to heat. It should also be noted that introduced insects may have a higher heat tolerance and that in some cases it is not always guaranteed that all pests in cracks and crevices can be reached. She concludes: “In a museum context, I couldn’t imagine any material that could be subjected to heat treatment without any concerns – possibly certain textiles. But I would also be cautious with this group of objects, especially with the available alternatives for pest control.” When asked, Rentokil explained that heat treatment is only carried out after careful risk analysis. Another tried and tested method is nitrogen fumigation, also known as anoxia. A room is first carefully sealed to prevent oxygen from entering from outside. Nitrogen is then introduced into the room using nitrogen cylinders or nitrogen generators. The nitrogen displaces the oxygen and reduces it to a minimum, thus ensuring that the pests suffocate. Leaving the art objects for a longer period of time guarantees that all insects die. Once the nitrogen treatment is complete, the room is ventilated to slowly bring the oxygen content back to normal. Nitrogen treatment also ensures that the artworks are preserved and there is no exposure to toxins contained in biocides. Pest treatment with nitrogen can be applied to paintings, sculptures, textiles, wood and much more, making it suitable for a wide variety of museums and collections. It is a method that is used by many renowned museums, as an expert from Rentokil tells us.

By the way: From July 3, 2025, the Staatliche Graphische Sammlung München will be presenting an extraordinary exhibition on images of nature in art – from ukiyo-e to contemporary installations.