Although Birmingham Museum Trust’s sites are closed currently, they are still attracting one group of visitors of a very unwelcome variety.
Museum collections contain many organic materials which are an ideal food source for insect pests; including paper, woollen costumes, wooden objects, fur & feathers, and silk. Additionally, museums and their stores are usually dark, and objects are left undisturbed for long periods, which is a perfect environment for pests.
Some of the most frequently encountered insect pests in museums are moths. One of the most common varieties of moth is the Case Bearing Clothes Moth - Tinea Pellionella.
Case bearing clothes moth adults are around 6-8mm long, and are brown with distinctly spotted wings.
Adult case bearing clothes moth.
Adult moths lay eggs, which hatch into larvae. The larvae feed and wrap themselves in cocoons made of the material which they are feeding upon; the larvae then carry their cocoons with them as they crawl around. Inside their cocoons they pupate into adults.
Larvae wrapped in cocoons made of food debris.
Adult moths don’t feed, and exist purely to reproduce. Ordinarily most insects breed in the spring or summer, but heated buildings allow insects to breed all year round, and the complete life cycle of a clothes moth can be a little as one month.
Typical evidence of case bearing clothes moths.
Often clothes moths will spend their entire lives walking rather than flying anywhere, so you may not ever see them in the air, or far from their food sources.
It is the larvae which do all of the damage - by the time you see the adults it is too late!
Some insect pests such as clothes moths no longer exist ‘in the wild’, and are now found exclusively alongside humans.
Part of the preventive work routinely conducted by Birmingham Museums's conservation team is monitoring for and eliminating pest infestations across the museum sites and stores.
With fewer people currently on site it is easier for the evidence of pest infestations to go unnoticed and so for damage to be caused to collections – so the preventive work carried out by the conservation team is particularly important in these times.
Recently an infestation of moths was discovered in a taxidermy collie dog on display at Thinktank.
Taxidermy collie dog.
Evidence of moth infestation found on the taxidermy collie dog.
Frass – fine granules of excreta (moth poo), and loose hairs caused by the moth larvae.
The dog was removed from the surrounding displays and carefully vacuumed to remove as many of the moths, cocoons, and eggs as possible.
Birmingham Museums Trust has a large walk-in freezer into which objects can be placed to treat pest infestations. The collie dog has been sealed in a polythene bag in order to isolate it and prevent any remaining moths from getting into other areas of the collection, and to prevent condensation forming on the object during the freezing process.
It will be cooled to a temperature of -40°C, which will kill off any remaining moths. It will then be monitored to ensure that there is no resurgence of the moth population, before eventually being unwrapped, vacuumed again, and returned to its place in the museum.
The collie dog sealed d in polythene.
The objects in the area surrounding the collie dog were inspected for signs of further moth activity. None was found; but they were treated with a water-based insecticide as a precaution, and will be closely monitored.
Pheromone lures were placed at intervals around the area in order to catch any moths which might be travelling further afield. They consist of a sticky sheet coated in the pheromones usually given off by female moths. Male moths will mistake the sticky sheet for a female moth (they’re not very bright) and get caught on it, allowing them to be examined.
A typical example of a moth pheromone lure.
There have been no catches in Thinktank so far, suggesting that the moth population was restricted to the collie dog.
While this infestation was quickly identified and has been contained; there will always be more uninvited pest visitors eager to try to munch on the collections. Luckily there will also always be a preventive conservator not far away and ready to save the museum’s objects from being eaten – even during the current period of lockdown.