Conserve O Gram 3/7: Monitoring Insect Pests with Sticky Traps

The goal of integrated pest management (IPM) is detection, identification, and eradication of pests before they become established and cause damage to heritage collections. Any animal is considered a “pest” when unwanted in a space. Insect pests that are known to target museum collections are informally known as museum pests or heritage eaters. Regionally common insects that do not eat collection materials but seek refuge inside buildings are considered nuisance pests. Although they do not eat collections, their presence can attract those that do, and they usually signal other environmental issues to address, such as dampness and unsealed points of entry. Regular visual inspection of collections storage and display spaces is an important part of an IPM program. Equally important are inspections of areas prone to being damp, dark, and/or near exterior doors and windows. However, since it is impossible to visually monitor pest activity constantly throughout the day, and after hours when activity tends to peak, sticky traps are used as a means of continuous monitoring.

Figure 1: Assembled blunder sticky trap placed against the wall (the typical travel route of pests) with ID and date facing outward. (NPS Photo)

Sticky traps are an effective complement to other components of a complete IPM program. They can catch both flying and crawling insects at various lifecycle stages. They provide a snapshot of pest activity for a designated area and time interval by preserving insect pest traffic information. This information includes the types of pests caught, their growth stages, and their volume by type. Over time, the cumulative information provided by the traps can help identify the emergence of an infestation, seasonal insect trends, and vulnerabilities in the building envelope. Traps are strictly a monitoring tool and do nothing to prevent or control an infestation. Note that sticky traps are only for use with insect pests. Vertebrates such as rats and mice should be captured using snap traps, which is considered the most humane method of trapping. For more information on developing a complete IPM program, see NPS Museum Handbook, Part 1, Chapter 5, Biological Infestations.

Description of Sticky Traps

A sticky trap is made from sturdy card stock, often in a triangular or wedge-shaped configuration with open sides. The interior base is coated with a non-toxic, non-drying sticky substance, and the trap is placed on flat surfaces such as windowsills or floors. Insect pests encounter the sticky surface and are caught in place. There is typically no form of attractant on this common trap, which is why it is also known as a blunder trap – the insect pests simply wander into them. There are larger, specialty versions of sticky traps with attractants formulated for a specific type of insect, such as those formulated exclusively for roaches. Other versions of the sticky trap are hanging tent traps and fly paper for flying insects, and window strips for insects attracted to sunlight. These may be useful in certain circumstances, such as in historic homes monitoring for nuisance pest Asian lady beetles.

Special Attractants

Pheromone lures that attract specific types of pests, such as clothes moths or cigarette beetles, are available to use in conjunction with sticky traps. In general, these are only recommended during an active and widespread infestation of a particular species, to attempt to pinpoint the “ground zero” food source. Pheromones are not recommended for regular monitoring, as they are expensive, have a limited shelf life, and most importantly may lure pests into the space to create a problem where previously there was none. Work with a museum professional with IPM experience if pheromone lures are needed, to ensure they are used properly.

Modifications to Prevent Vertebrate Catches

Figure 2: Example of a modified sticky trap, used by a park to prevent catching lizards by blocking them with plastic chicken wire mesh, attached via zip ties. The modification can be removed from the trap and reused on a fresh one. (NPS Photo)

Modifications can be made to sticky traps to prevent catching vertebrates such as snakes, lizards, and mice. Sticky-lined plastic boxes that have small openings to prevent vertebrates from entering may be purchased from pest control companies for this purpose. Cheaper versions can be made by hand by adding materials such as plastic chicken wire mesh or garden fence to the opening of blunder traps via a plastic zip tie (see Figure 2).

When choosing a preventive measure, ensure the webbing/opening is large enough for insects to travel through, yet small enough to prevent vertebrates. Note that mice can squeeze through openings as small as ¼ inch. To save time and resources, only modify traps in locations where vertebrates are known to be blundering by. For example, an exterior door where mice have been accidentally caught in the past.

Setting the Traps

Before setting out traps, plan the trap locations and use the same spots each month to track issues over time. This can be done easily using a printed building floor plan or a simple drawing of the building layout with features included such as doors, windows, vents, or other potential entry points. Mark the position where each trap will be placed using the following guidelines that consider typical travel patterns, harborage, and food or water sources:

• Abutting the wall/floor junctions at intervals of 5-10 m (16-33 ft), depending on the room size. Traps should be flush against the wall to ensure passersby will encounter the sticky surface.

• In corners, near doors, vents, fireplaces, or any potential entry point for insects.

• In dark, hidden areas that are difficult to see and not often disturbed.

• On windowsills, flush against the window or adjoining wall (if in an alcove).

• In exhibit cases (where permissible) and storage cabinets containing vulnerable materials such as those made of protein like wool and fur. Traps in these locations should be placed in a configuration that ensures the sticky surface will never endanger museum objects.

Understand that trap locations may need to be added, removed, or reorganized depending on insect pest activity, changes in building activities, or overall IPM program objectives. Be sure to reflect this in trap tracking and numbering. For example, if over a year of monitoring you notice one room never has catches on several traps, you may reduce the number of traps in that room to save time and resources. Or, if you notice that a windowsill is more active than a doorway, you may move the doorway trap to the windowsill, changing the ID number to prevent confusion.

After trap locations are determined, each should be designated with a unique ID number. The IDs should be part of a consistent naming system to accurately compile catch data. One method in developing a naming system is to use the room name followed by a number. For instance, for a storage room, three trap locations could be named S.1, S.2, and S.3. Likewise, a room number (if there is one) may be used; the traps in Room 101 could be named 101.1, 101.2,101.3, etc. A naming convention that includes a decimal and number extension, as in the examples above, allows for expansion and/or reorganization of traps depending on pest activity without disrupting the entire system. The naming system must be consistent throughout the site for it to be successful.

Write the date and ID numbers on the sticky traps using a permanent marker or pen before assembling them. Follow manufacturer’s guidelines, but typically setting up traps is easy: the scored paper is folded, the film over the sticky area is removed, and the tab is inserted into the top. The use of a cart or handheld tray will help make distributing (and collecting) traps easier. Traps should be placed on flat surfaces against a wall or window frame with date and ID number side facing outward for quick identification (see Figure 1).

The number of traps per room depends on the size of the room, the number of windows and doors, materials stored in the room, and – most importantly – the number of staff available to check the traps. Setting a trap at every possible point in a room is useless if staff cannot check it on a regular (i.e. monthly) basis. Instead, start with the number of traps that one can reliably check, and add to that, if needed.

Recording Catch Data

The traps should be inspected on a regular basis and the catches recorded. When initiating an IPM program or after treatment for an infestation, traps should be checked weekly. Under normal circumstances, it is common to collect traps and record catches monthly. Each site will determine the appropriate time interval between recordings in alignment with their complete IPM plan. The data that should be recorded from the traps are as follows:

• The species of insect pest and its approximate life stage.

• The number of the species caught. The direction from which it entered the trap (if relevant).

There are many online resources for identifying insects which can help to distinguish between heritage eaters and common nuisance pests, such as MuseumPests.net. Under normal circumstances, traps will be mostly populated with common nuisance pests and few heritage eaters, so it is recommended that staff become acquainted with common local species. There may also be pests harmful to human health that the IPM coordinator should be able to quickly identify, such as brown recluse spiders.

Traps that have no catches may be re-used for another monitoring period, but caution must be used. The trap’s surface may lose its stickiness and become covered in dust, dirt, and debris over time, reducing the trap’s effectiveness. Also, traps containing dead insects left for an extended time will become a food source for other insects that are heritage eaters.

Figure 3: Example of recording trap catches in a spreadsheet that notes the date, room name or number, trap ID, catches, and notes, if applicable. (NPS Photo)

Catch data can be recorded in a dedicated notebook, spreadsheet, or database (see Figure 3). It is helpful to also write a prose paragraph summarizing the month’s catches, as well as environment and other pertinent information in a continuous document. Catches in unintentional traps such as light covers, light diffusers, vases, and windowsills can also be discussed in prose. The running narrative style of recording pest information contributes to a more comprehensive IPM analysis that goes beyond numbers on a spreadsheet. These elaborated records will assist observers to better assess what they are seeing and holistically understand insect pest activity at their site. The document should be easily accessible to all museum staff and can help spread awareness of areas of concern and may be used to teach pest monitoring principles.

The following is an example of a pest catch monthly summary for a collection storage room in a winter month in the eastern U.S.:

“Pest numbers remained steady from last month at 217 catches. The seasonal decline in pests was halted by a resurgence of springtails. An increase in other shoulder season pests, such as midges, mites, and ground beetles were seen as well. These unseasonable catches were due to several spells of unexpected warm and wet weather this month. Silverfish numbers increased to 16 from 10 catches in November, which is consistent with the wetter weather. Dermestid activity is still low with only 1 larva caught.”

Interpreting Catch Data

The catch details recorded from the traps will provide a variety of invaluable information:

• Identification of individual insect pest species will indicate if the intruders are heritage eaters or nuisance visitors.

• The number of a particular species caught over time will indicate whether an infestation has become established or is an isolated, minor outbreak.

• The stage of development (larva or adult) may give insight into an infestation. Larvae indicate an active local infestation due to their limited mobility, while adult insects may be mobile, newly entering pests.

• A concentration of insects in one area of trapping and/or insects entering a trap from a preferred side may indicate where an infestation is focused.

• The contents of traps after an infestation treatment can indicate the treatment’s success or failure. Keep in mind the life cycle of the species and monitor traps for several months before declaring a site infestation-free.
  

Insect pest monitoring is a valuable component of a complete IPM program and can be an early warning sign of danger to heritage collections. Collecting and saving monthly pest data helps to understand a site’s overall insect pest activity and provide data for monthly and yearly comparisons. Each pest has an “action threshold” or a quantity of that species that when reached, requires action to mitigate a potential problem. See the NPS Museum Handbook, Part 1, Chapter 5, Biological Infestations for sample action plans of specific pests.

For further information on Pest Management see Conserve O Gram 3/6 An Insect Pest Control Procedure: The Freezing Process and Conserve O Gram 3/8 Controlling Insect Pests: Alternatives to Pesticides. To help recognize pest activity on museum objects, see Conserve O Gram 3/11 Identifying Museum Insect Pest Damage and Conserve O Gram 3/12 Identifying Mouse and Rat Damage in Museum Collections.

Selected References

MuseumPests.net/identification

NPS Museum Handbook, Part 1. Chapter 5, Biological Infestations. 2014.

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Fran Ritchie, Organic Objects Conservator and IPM Coordinator
Ray Mansfield, Conservation Technician
Kyle Bryner, Conserve O Gram Coordinator and Editor/Museum Specialist and Collection Manager
Shay Henrion, Registrar and Conserve O Gram Editor
Museum Conservation and Collections
Harpers Ferry Center, National Park Service

Formerly issued as Conserve O Gram 3/7 Monitoring Insect Pests with Sticky Traps
R.E. Child (1998), Head of Conservation and Advisor on Insect Pest Control
National Museums and Galleries of Wales

The Conserve O Gram series is published as a reference on collections management and curatorial issues. Mention of a product, a manufacturer, or a supplier by name in this publication does not constitute an endorsement of that product or supplier by the National Park Service. Sources named are not all inclusive. It is suggested that readers also seek alternative product and vendor information in order to assess the full range of available supplies and equipment.

The series is available on the National Park Service Museum Management Program's website.