The Mystery of the Tasty Canvases

So why do insects and other pests attack art collections? Bugs generally do not eat oil-based paint or ground, which has no nutritional value to them, but they do tend to like plant- and animal-based materials, which is what canvases and paper labels are made of. Some creatures, like termites and powderpost beetles, love to eat wood. I wanted to determine what type of fibers were used to create Lasekan’s canvases, to see if there was a reason that I only found signs of insects on them, and not on other canvases. SoI took small fiber samples from the edges of the canvases and examined them under a microscope to identify the fibers present. I did not find wool as I had theorized, but instead the canvas seemed to be comprised mostly of cotton fibers. This could explain why the bug-eaten areas were all quite small, as the larvae could have tried out these materials, but quickly moved on to more suitable food sources.

Next, I wanted to try to identify the species which had caused the damage, to better understand its life cycle, and keep an eye out for other forms of the pest. The website MuseumPests.net is an excellent resource to use for this process, as it has a searchable image library containing pictures of the various life stages of many different insects. It seemed to me that the Black Carpet Beetle larva pictured at right (from Jim Kalisch, UNL Entomology) closely resembled the segmented casing remains that I had encountered on the backs of the paintings.

Further research into this pest showed that though they are primarily attracted to animal based materials (wool, fur, felt, silk, feathers, etc), it is the larvae which graze on these materials as they grow and molt. The larvae can grow up to 5/16 of an inch and can live 6 to 12 months before pupating. The good news is that once the larvae pupate and become adults, they no longer eat the same materials, but prefer pollen and nectar for food, so they are generally found outdoors. 

So how do conservators mitigate pest infestations and prevent them from happening or worsening? Mitigation is different than you might expect. The typical pesticides that you would use in a home or business are quite toxic and can be damaging to artworks, as residues are often left behind. So instead, conservators use safer but equally effective treatments like freezing, anoxia, or nitrogen chambers. Freezing an object with active bugs inside can be effective at killing them, if low enough temperatures are reached for a sufficient duration, but the cycle of thawing could lead to cracking of some materials, so it is not always the best choice. Anoxia involves creating a sealed container to fit the artwork, usually using a thick plastic or foil, and removing oxygen from it with “oxygen scavengers” (at left).

It is difficult to recommend guaranteed ways to prevent pests from affecting collections at all. Their often very small size, ability to attach themselves unseen to clothing or boxes, and life cycles that include dormancy all make this agent of deterioration particularly insidious. Most institutions follow a policy of Integrated Pest Management, which involves using the most economical and least hazardous means of controlling pests proactively. Consistent monitoring is essential for early detection of any pests, especially in collections with lots of hair, wool, wood, or other organic materials. You can use pest traps like the one pictured below, which should be placed along the base of walls, to see if there is a common type of bug found in buildings or storage areas. Careful examination of any new items entering a collection, and isolating anything suspected of having pests are also important tactics. However, it is highly recommended that you hire an expert, such as a conservator focused on preventive care, to assess any areas or objects of concern.