Friday, 15 February 2013

Every Conservators' Nemesis...

Pesticides are now no longer routinely used on our collections.  My colleague Kate Jackson, conservator at the Pitt Rivers Museum, has written a post about our current pest management systems:

1923.85.293 Textile from Nagaland, N. India, with active moth infestation

In the past, museum collections were routinely treated with pesticides in an attempt to stop the damage caused by moth, beetle and wood boring insects.  The Museum's Annual report dated 1906 boasts – ‘the addition of a fuming-room, in which specimens infected with moth and beetle may be cured, will be of great convenience, and will greatly lessen the trouble caused by insect depredations’.

Unfortunately there was no 'miracle cure’ and as it transpired the commonly-used pesticides have over time proved to be highly hazardous not only to insect pests but also to us humans and in some cases to the objects themselves. Due to the health and safety issues surrounding the use of pesticides in museums they are no longer widely used, and we must instead find alternative methods of warding off unwanted insect pests.

Up to eighty percent of the Pitt Rivers ethnography collection is made up of objects composed of organic materials such as textile, feather, fur, hair, wool, felt and skin. It is these organic materials that attract every conservator’s nemesis - the common clothes moth (Tineola bisselliella). Due to warmer winters and the decline in pesticide use over past decades the cloths moth has enjoyed a population boom within UK museums. In order to tackle the issues of moth in museums it is vital that we understand what we are dealing with.

Adult common clothes moth

The adult moth, which prefers dry, warm, dark areas, lives for between 70-80 days. The female lays her eggs within undisturbed, organic materials.  As the larvae hatch they feed for between 2-30 months (depending on environment) on any organic material close by. It is this larval stage that can cause devastation to museum objects if left undiscovered. The larvae will eventually cocoon before the adult moth emerges after 8-10 days.

There are 35 pheromone moth traps within the museum, the majority within high-risk cases, with others placed in open areas. The pheromone used on the traps attracts the male moth and the sticky surface holds the moth in the trap. Every week a conservator checks the traps and counts the number of moths caught. The number will indicate if there is a gradual or sudden rise in moth in the area, this will lead us to do a thorough search of the surrounding cases. If an outbreak is found the objects infested are sealed in bags and placed in one of our chest freezers at -30 for three days. This temperature will kill every stage of the moth whether adult, egg, larvae or cocoon. The conservator will then assess the objects, any pest debris will be removed and any damage recorded.

We also have a number of ‘blunder’ traps. These are also sticky, and would hold a blundering beetle if it wandered across the trap. Thankfully we have not had major problems with beetles or wood boring insects for a number of years. If we were to find an outbreak we would use the same freezing method, which would kill the beetle at all stages of its life-cycle.

An unaccessioned Biddenden Biscuit, with biscuit beetle damage.