Museums waging war on exhibit-eating bugs
Collections of irreplaceable and valuable artefacts in many of Britain's museums and heritage properties are under threat from a growing army of insects, particularly moth and beetle larvae. Can we stop them munching away on our precious relics?
"If you have ethnographic objects from around the world which were collected maybe 200 years ago, maybe some of these people are no longer producing these objects, maybe some have even died out... you can't just go and get another one."
"Bug man" David Pinniger, an entomologist and renowned heritage site pest control consultant, knows how important it is to put an end to an infestation before the damage becomes irreversible.
He is the person Britain's biggest museums call when conservators make the terrible discovery that one of the nation's exhibits has become lunch for some bugs.
He works with all Britain's national museums, as flourishing populations of a pest called the "clothes moth" have been causing havoc in recent years.
"Virtually all the major museums now have clothes moths, and some serious problems, where 10 years ago we found very few indeed," he says.
Webbing clothes moths are about 8mm long and gold-ish in colour, but Mr Pinniger explains that people should not be fooled by their size: "People find big moths and think they do lots of damage, but clothes moths are really small."
The Pitt Rivers Museum, which is home to Oxford University's collection of anthropology and world archaeology, was recently forced to call on his services.
Heather Richardson, head of conservation at Pitt Rivers, says: "We have a much higher density of objects on display than a lot of other museums do. In a fine art institution you may have five objects in one case - we have 300 in it."
The museum has always had a few clothes moths, but in 2005 they took hold of one display case and despite treating the case straight away, the problem spread to other cases.
Ms Richardson says there is a key reason moths love their displays: "These cases are full of natural fibres, hairs and skins - food potentially for beetle and moth larvae."
Adrian Doyle, collections care conservator at the Museum of London, has to keep a close eye on exhibits he classes as high on the "munchability index".
"The things most munchable are things probably most valuable, like wool, silk, cotton, older fabrics," he says.
The museum is home to the Fanshawe dress, which belonged to the Lady Mayoress of the City of London in 1751.
Mr Doyle says: "It is absolutely beautiful and highly munchable - so the risks to that are extreme and we keep a very, very close eye on it indeed.
"We have an enormous costume collection here, and if we had a couple of moths in there I would be extremely worried because they multiply so quickly, and before you know it we've got an epidemic on our hands."
David Pinniger says the nooks and crannies in historic buildings provide perfect hiding places. "To get on top of pests, you need to think like an insect. If you are a clothes moth, you want it dark, undisturbed and nice and warm, and that's the place you want to be looking."
So why are the numbers of clothes moths increasing?
Mr Pinniger says: "Everyone's shouting climate change. Because we've had a lot of warmer winters, we're often running our buildings warmer inside now, but there's also the fact that we have lost some pesticides that were very effective against clothes moths and we can't use them now."
Pesticide dichlorvos, which was used in museums to kill insect pests for years, was banned after being found to be carcinogenic.
Val Blyth, the conservator at the Victoria and Albert Museum, says there was a population explosion of webbing clothes moths throughout London three to four years ago, and agrees the loss of chemicals has hampered eradication efforts.
By using moth lures, her team found moths at the V&A were living off debris that fell into a void underneath floorboards in the British Galleries' wood-panelled rooms.
Adrian Doyle has a theory about why insect numbers are up. "When I was a kid, if you went to a museum and it was cold in winter you wore a coat. Stores were cold in winter, so insects died."
But pest specialists are also using modern techniques to assess how bad an infestation is and deal with it.
At Pitt Rivers they are trying pheromone traps, using female pheromone to attract males.
Mr Pinniger explains: "There's a glue board inside which is sticky. The board contains this glue... and a pheromone equivalent to 1,000 female moths, so these poor deluded males are attracted to that [pheromone] and then get stuck in the trap."
Dee Lauder works for English Heritage Collections Conservation as its collections care manager.
At Dover Castle, a lot of the pests are damp-related. The Kings Hall there is covered in red woollen wall hangings. She says: "The dye that they used for that, carmine, was basically made from crushed insect bodies.
"We've laid out realms of protein for the insect pests to feast upon. It's a steak house." And in gaps and cracks behind the wall hangings, insects can live without being disturbed.
She is using a moth confusion lure, called Exosex, which coats males moths in a female pheromone when they enter it, ensuring they attract other male moths once they fly back out, interrupting the breeding cycle.
But she says the simplest solution is often the most effective. "It all depends on whether it's a major infestation. In most cases a lot of it is down to good housekeeping," she says.
Val Blyth says freezing individual objects at a very cold temperature also kills bugs.
"What I do as a preventive method, or to treat an infestation as we do, is put things wrapped in our chest freezers, and take the temperature down to -30, and over a period of three days this will kill most insect pests."
When David Pinniger retires, a small group of conservators will continue working to protect Britain's museums from hungry insects. They plan to discuss their strategies at the Pest Odyssey gathering at the British Museum in October.
What's Eating the Museum is on BBC Radio 4, Wednesday 31 August at 11:00 BST.